Good Gardens With Less Water - Australia

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  • 1. GOOD GARDENS WITH LESS WATER
  • 2. GOOD GARDENS WITH LESS WATER K EVIN H AN D RE CK CSIRO PUBLISHING GARDENING GUIDES
  • 3. © Netherwood Horticultural Consultants Pty Ltd 2008All rights reserved. Except under the conditions described in the Australian Copyright Act 1968 and subsequentamendments, no part of this publication may be reproduced, stored in a retrieval system or transmitted in anyform or by any means, electronic, mechanical, photocopying, recording, duplicating or otherwise, without theprior permission of the copyright owner. Contact CSIRO PUBLISHING for all permission requests.National Library of Australia Cataloguing-in-Publication entry Handreck, Kevin, 1938– Good gardens with less water/author, Kevin Handreck. Collingwood, Vic.: CSIRO Publishing, 2008. 9780643094703 (pbk.) CSIRO Publishing gardening guides Includes index. Bibliography. Landscape gardening – Water conservation – Australia. Drought-tolerant plants. 635.0994Published byCSIRO PUBLISHING150 Oxford Street (PO Box 1139)Collingwood VIC 3066AustraliaTelephone: +61 3 9662 7666Local call: 1300 788 000 (Australia only)Fax: +61 3 9662 7555Email: publishing.sales@csiro.auWeb site: www.publish.csiro.auFront cover (clockwise, from top right):Leucospermum gerrardii; image by iStockphoto; Stylidium elongatum; terracing on a steep slope;Italian capsicums; image by iStockphoto; image by iStockphotoBack cover (clockwise, from top right):Drainage pipe; Dryandra formosa; Yates Tuscan planter; a potted agave; cherry tomatoesSet in 10.5/14 Adobe ITC New BaskervilleCover and text design by James KellyTypeset by Desktop Concepts Pty Ltd, MelbournePrinted in Singapore by ImagoAll illustrations in this book are by the author unless otherwise acknowledged.Note: For simplicity, some trade names are used in the text of this book or can be seen on illustrations.No endorsement of these products is intended, nor is criticism implied of similar products that are notmentioned or illustrated.
  • 4. CONTENTSPreface viiAcknowledgements ix 1 Causes of water shortages 1 2 Plants and water 5 3 Know your soil 29 4 Organic matter and soils 39 5 Your soil is a reservoir 45 6 Water quality 55 7 Delivering water to your plants 67 8 Garden watering systems 85 9 Mulches: the facts 9510 New gardens and new gardens from old 10511 Dealing with too much water 11312 Lawns 11713 Water for plants in pots 13114 Testing potting mixes 147Appendix 1 Sources of extra information 150Index 153 v
  • 5. Grevillea ‘Superb’ is a showy cross between G. banksii and G. bipinnatifida that is best suited to warm temperateareas.
  • 6. PREFACEDuring the last 10 years or so, gardening in much as the global warming to which we allof Australia has become more difficult. Water contribute bites harder. If we want to have therestrictions have progressively become more many benefits that gardens provide, we need tosevere as drought has intensified its grip on all of make the most of the water that is available toour largest cities and their hinterlands. These us. That means using ALL the water that isrestrictions have progressed from mild (watering provided free to us via rain, and recycling toallowed every second day or three times a the garden as much as possible of the waterweek), through once-a-week watering via that we use in our homes.drippers – to, in increasingly large areas, bucket I want to show you how it is possible to have aonly, and in others, a total ban on the application lovely garden even when water restrictions areof municipal water direct to the garden. severe. The knowledge contained in this book,Gardeners might argue that these restrictions supplemented where appropriate withare unfair, as they do not always address water information freely available on the websitesuse by industry and within the home. But listed, will, I am sure, enable you to do this. Ibefore you get too agitated, spare a thought for will show you that with a little thought andirrigation farmers, some of whom have had to some effort, it is possible to have a beautifulwatch their life’s work die because their water garden almost anywhere in Australia even withallocation has been slashed. the most severe restrictions on the use of water from municipal supplies.Water shortages are likely to get worse in allparts of Australia except the far northern tropics There are several sets of characters in this book. The central character is water. It is essential to all life. Waters from different sources are not all created equal though; they come with different amounts of dissolved salts and sometimes other contaminants. One part of this book will show you how to assess water from different sources and how to use this information when you use these kinds of waters in your garden. The characters of the second set are almost beyond counting. They are the many thousands of plants that you can choose from to produce the visible part of your garden. They will notAlmost every edition of every Australian newspaper thank you if you have put them in anhas at least one article about water. environment they do not like. Life will be vii
  • 7. easiest for you as their carer, and for them, if source of carbon dioxide, without which thereyou have chosen only plants that like your are no plants. The second provides the energysoil and climate, and that manage with the that is essential for plants to use carbonamount and quality of water that you can dioxide, take up water and grow.provide to them. There is of course another character – you, thePlants get most of their water from the gardener. It is you who will enjoy the gardenmedium in which they are growing. This that you have created out of water, plants andgrowing medium will generally be a soil, soil. It is you who may well have a longer andsometimes natural, sometimes a blend more satisfying life because of your efforts. It isproduced by a soil supplier. It could also be a you who will know that your garden is soakingpotting mix. To allow your plants to get the up some of the extra carbon dioxide that is themost out of the water you or rain provide to major cause of the water shortages we arethem, it is desirable that you understand experiencing in Australia. You know that you aresomething of the interaction between water providing oxygen for yourself and others throughand growing media. The third set of characters the plants of your garden.of this book is therefore soils and othergrowing media. Their ability to hold and Enjoy your garden.supply water is fundamental to having a good KEVIN HANDRECKgarden, even with less water. Managing Director, Netherwood HorticulturalA couple of invisible characters support the Consultants Pty Ltd, Adelaide,others. These are air and light. The first is the and former CSIRO Soil ScientistIf only we had this much water in southern Australia! Victoria Falls, Zimbabwe–Zambia border.viii GOOD GARDENS WITH LESS WATER
  • 8. ACKNOWLEDGEMENTSThis book was initiated by my publisher – Ted Queensland; Jon Lamb, Jon LambHamilton – of CSIRO Publishing. I thank him Communications; Simon Leake, Sydneyfor persisting against my initial reluctance and Environmental and Soil Laboratory; Lesleyfor his expert guidance. Retirement for both Lopez, Burke’s Backyard Magazine; Timpublisher and author is no barrier to Maguire, Toro Australia; Basant Maheshwari,accomplishment. This book could not have CRC for Irrigation Futures; Don Marriott,been produced without the help I received Advanced Irrigation Consultants; Johnfrom many individuals and organisations. I am McDonald, Nursery & Garden Industryparticularly indebted to the following. Queensland; Mitre 10, Malvern, South Australia; Tom Morley, DPI Victoria; JohnRob Bickford, CSIRO; Kate Blood, Department Neylan, AGCSA; Jann O’Connor, Irrigationof Primary Industries, Victoria; Keith Bodman, Australia; Bob Patterson, Lanfax Laboratories;Rio Tinto; Chris Brady, Bureau of Metereology Chris Pfeffer, DNRW, Brisbane; Tony Robinson,(BoM), Adelaide; John Brennan, Water Sydney Water; Therese Scales, TikalaraCorporation, Western Australia; Don Bromley, Designs; Chris Smith, Weathermatic Australia;The Container Connection; Bruce Brooks, Diana Snape; Richard Stirzaker, CSIRO; NathanBoM, Adelaide; Bunnings, Mile End, South Syme, Jeffries; Greg Thomas, McCracken’sAustralia; Jolyon Burnett, CEO Irrigation Water Services; Tony Thomson, Department ofAustralia; Butlers Irrigation, Adelaide; Bob Water, Land, and Biodiversity ConservationCampbell, Sage Horticulture; Colin Campbell; (DWLBC), South Australia; Thelma andIan Chivers, Native Seeds Pty Ltd; Geoff Malcolm Vandepeer; Gerard White,Connellan; Geoff Cresswell, Cresswell Payneham Plant Wholesalers; Troy Whitmarsh,Horticultural Services; Ken Cuming, Reece Irrigation.Moisturematic Controls; Bianca Dimont, My special thanks go to my wife Eleanor, whoDepartment of Natural Resources and Water critically reviewed the several drafts, and(DNRW), Brisbane; Tim Durham, Eynesbury; insisted that I write clearly and logically. NoSid Dyer, A2Z Planter Technology; Rodger weasel words, marketing-talk or sloppinessElliot; Kathy Errey, Payneham Plant were permitted.Wholesalers; John Gransbury, Hydroplan; CliffHignett, Soil Water Solutions; Des Horton, CityWest Water; David Huett, New South Wales KEVIN HANDRECKAgriculture; Daryl Joyce, University of Adelaide, September 2007 ix
  • 9. A major cause: people and their machines. (Photo: Ted Hamilton)
  • 10. C AU S E S O F WAT ER S H O R TAG E SThere are three major causes for the current rainfall across southern Australia, butrestrictions on water use in our gardens. increased rainfall in the tropics and in parts of central Australia (see the references listedThe main cause is reduced rainfall, which in in Appendix 1 for detailed information).turn is due to the increasing concentrations of Scientists have shown that when rainfallthe greenhouse gases carbon dioxide, nitrous decreases by 10%, there is 30–50% decreaseoxide and methane in the atmosphere. The in runoff into streams and reservoirs. Thecarbon dioxide and nitrous oxide come from trend towards decreased rainfall startedour burning of fossil fuels – coal, oil and gas – about 25 years ago in south-western Westernthat produces the energy we use for heating Australia and, more recently, in south-easternand cooling, for running our appliances, and Queensland, but it is now universal infor powering our factories, vehicles and southern Australia.aeroplanes. The methane comes from ricepaddies, cattle, rubbish dumps and, There is therefore a direct link between ourincreasingly, from peat bogs as they thaw, and use of energy and lower water levels in ourdeep ocean deposits as ocean temperature reservoirs. And because Australians use morerises. The higher the concentration of these energy per person than do the citizens of anygases in the atmosphere, the greater is the other industrialised country, we are majorreduction in the loss to space of heat contributors to our lack of water. More widely,generated when the sun’s rays hit the earth’s the combination of rising living standardssurface. The resulting rise in the average throughout much of Asia and the Middletemperature of the lower atmosphere East, and rapidly increasing populations, isincreases evaporation of water. Water in the bringing billions of people in these regionsatmosphere is a powerful greenhouse gas, so up towards our energy use and greenhousethe warming is further increased. gas production levels.One result of increasing atmospheric A second cause of water restrictions istemperature is that circulation patterns in the increasing population. At a local level, theatmosphere shift. This means lower average combination of increasing population with 1
  • 11. 50.0 40.0 30.0 20.0 15.0 10.0 5.0 0.0 -5.0 -10.0 -15.0 -20.0 -30.0 -40.0 -50.0 Trend in annual total rainfall 1950–2006 (mm/10 yrs)Australian rainfall trends, 1950–2006. (Bureau of Meteorology)drastically lower water levels in reservoirs has decreased amount of water used inan inevitable result. gardens, generally with minimal effect on plant qualityA third cause is lack of vision by some voluntary reductions in energy use bypoliticians. The first warnings about global increasing numbers of peoplewarming and its possible consequences were general acceptance and practice of shortermade by scientists nearly 40 years ago. Solid showers and many other water-savingevidence has existed for at least 15 years, yet measuresthe leaders of countries whose citizens are the reduction of carbon footprint by parts ofbiggest polluters have taken little action until Australian industryvery recently. Even now, when the evidence is small increase in the proportion of totalas solid as anything can be, much of the energy production from wind, the sun,political response is nowhere near what is geothermal sources and wavesnecessary to avert catastrophe for our phasing out of incandescent light bulbsgrandchildren. improved energy efficiency in electrical appliances purchase of carbon offsets to plant treesSome hopeful signs and generate green energyDespite the size of the problem, there are some moves to require energy efficientmany hopeful signs: design for new homes and other buildings2 GOOD GARDENS WITH LESS WATER
  • 12. slight decrease in average distance suggested that there should be an ‘oxygen travelled by private car tax’ imposed on non-gardeners! some increased use of public transport, Food produced in a home garden, even if it motor scooters, bicycles and feet. is only a few herbs and salad greens, saves the energy required to transport it from distant farms to local shops. Recycling ofGardens are a part of the cure food scraps through compost binsGardeners make a significant contribution to eliminates the energy cost of taking themreducing the effects of global warming. About to a landfill. Time spent planting,70% of the green cover in our cities is in trimming, weeding and sweeping by handhome gardens. The main environmental in the garden is time that might otherwiseeffect of this greenery is that, by providing have been used in energy intensiveshade and natural evaporative cooling, it activities such as driving or watchingcools the area around our homes in summer, television.so reducing – even eliminating – the need for Gardens are places for relaxing from theenergy hungry air conditioning. stress of modern life. Anyone who has visitedOur plants soak up carbon dioxide and the slums or ‘concrete jungles’ of many citiesrelease oxygen back into the atmosphere. soon learns to appreciate the softening effectGardening broadcaster Colin Campbell has that living plants have on a cityscape.Our cities do not have to become almost treeless, as in dusty Iqueque, Chile. (Photo: Eleanor Handreck) 1 – CAUSES OF WATER SHORTAGES 3
  • 13. Also, by creating a pleasant setting for their home, gardeners increase its value by up to tens of thousands of dollars. They create employment for at least 50 000 Australians through their purchases of plants, fertilisers, tools and landscaping services. They provide habitat for birds and other wildlife. And on average they live longer and healthier lives than non-gardeners. So before you feel guilty about using some of your allocation of municipal water in your garden, think of all the benefits you are providing to yourself, your family, your Still enjoying gardening at 87. community, our Earth.4 GOOD GARDENS WITH LESS WATER
  • 14. PL A N T S A N D WAT ER KEY POINTS Types of plants How to select plants that are suited to your climate, environment and soil How to avoid plants that might become weeds Water use and the three types of photosynthesis used by plants Roots and mycorrhizal fungi How plants get water and cope with drought Fertilisers and water use Phosphorus-sensitive plantsThere are at least 420 000 different types of environments. That is what we are doing inplants on our planet, of which at least 25 000 our attempts in Australia to reproduce theare native to Australia. Through the gardens of northern Europe. Restrictionscombined forces of changing climatic and on water use are doing to this style ofenvironmental conditions (cooling, heating, gardening what catastrophe did to thedrying, wetting, etc.), differing soil dinosaurs.properties and genetic mutation, each We can grow those plants that are eitherexisting plant is the product of an indigenous to our area (the native plants ofevolutionary process that has left it superbly our area), or come from other areas, bothadapted to a particular set of climatic and soil within and beyond Australia, whose climatesconditions. For a plant to grow well in our and soils are broadly similar to ours. For anygarden, we must provide it with conditions given area in Australia, this still gives usthat are reasonably close to those its parents many thousands of plants from which tohad in their natural environment. We can do choose. This style of gardening uses plantsthis in two ways. which, once established, will grow well andWe can use large amounts of energy and look good with little extra water than iswater to modify our garden so that it is provided by rain. Any extra water needed cansuitable for plants from very different come from water stored from runoff from 5
  • 15. Pansy – an annual plant.roofs and recycled from within the house.Much of any stored rainwater might well beused for producing fresh herbs, vegetablesand fruit.Types of plantsAll plants fit into one of three categories:1. Annuals grow from seed to producingseed to death within one year. Many gardenweeds are annual grasses. Many of thebedding plants such as pansies, petuniasand marigolds sold in garden centres areannuals. Shallow roots mean a need forfrequent watering in dry weather. Water Alternatives to drought-sensitive perennials (fromrestrictions and the unwillingness of many top): Pelargonium spinosum, Dryandra formosa,gardeners to take the time needed to plant Darwinia macrostegia.and maintain them have led to a rapiddecline in their use in home gardens in 3. Perennials grow for many years, oftenfavour of perennials. flowering and producing fruit or spores annually. In its broadest sense, this term2. Biennials need two years to complete their encompasses all trees, shrubs, ferns, bulbouslife cycle. They use the first year to produce and tuberous plants, the many smallthe framework for the flowering of the second herbaceous plants and the rhizomatous andyear. Parsley is an example. tussock-forming grasses. In gardening circles6 GOOD GARDENS WITH LESS WATER
  • 16. the term ‘perennial’ is generally restricted torefer to clumping herbaceous plants whosetops die back after flowering, but which grownew tops the following year.Basic decisionsAs a general rule, garden maintenance iseasiest when perennials, in the broadest sense,form all or the larger part of the plantings.There are several basic decisions to makewhen choosing perennial plants. One is to The small Eucalyptus dolichorhyncha (wasdecide on the relative contributions that E. forrestiana ssp. dolichorhyncha) gives a spectacularfoliage and flowers will make to your garden. year-long display and will fit into almost any garden. (Photo: Rodger Elliot)As the foliage of any plant will be present fora larger part of a year than will flowers, thecolour, texture and form of foliage is a major outdoor living areas, and will not dominateconsideration when choosing plants. descending layers of lower-growing shrubs.Another decision is about trees. A major You must also decide which trees need to bebenefit of trees in a garden is that the shading deciduous and which evergreen. Deciduousand cooling they provide reduces, even trees planted on northern and western sideseliminates in some areas, the need to use of the house provide shade in summer, but letenergy hungry air conditioning. A second the sun warm the house in winter.benefit is that trees enhance the appearanceof your home. A major problem is that thegarden areas around many new single houses How plants cope with differences inand townhouses are too small to allow the water supply and evaporation potentialgrowing of trees that will become very large Many of the different forms that we see inwhen mature. In any case, such large trees plants have evolved in response to the amountwill use so much water that smaller plants will of water available to them and/or to theneed extra watering if they are to survive. ability of the air in their native habitat toBut you can have your cake and eat it. There evaporate water. Here is some informationare many trees, including the smaller about the characteristics that have evolved ineucalypts (see http://asgap.org.au/gallery. plants to enable them to thrive in six differenthtml) and increasing numbers of grafted climatic zones. This information will help youeucalypts with guaranteed flower colours, choose the kinds of plants that will thrive inthat are of low to medium height (3–5 m) your garden. Table 1 at the end of this sectionwhen mature. These can shade walls and has a summary. 2 – PLANTS AND WATER 7
  • 17. Climatic zones with very high evaporation potential and little water At another climatic extreme are the plants of areas like the Atacama desert of southern Peru and northern Chile (annual rainfall near zero, but some fog along the coast); the Namib desert (20 mm rain and 50 mm from coastal fog); the Great Karoo of South Africa (annual rainfall about 100 mm); Baja California and nearby parts of south-westernPlants with large leaves tend to come from constantly USA. Annual evaporation can exceedmoist areas. 4000 mm. The plants of these areas are geared to rapid absorption of water when itClimatic zones with ample water and arrives, and to hanging onto it. They may below evaporation potential cacti, whose leaves have been transformed into spines and whose fluted stems minimiseAt one climatic extreme are areas where heat load, have chlorophyll and hold largeannual rainfall is higher than annual amounts of water.evaporation potential and there are no verylong dry periods. These include far Other water-storing plants are succulent.northern latitudes, southern Chile, high- Some stem succulents have no leaves at all;altitude areas elsewhere, and the wet tropics. photosynthesis takes place in their greenThe leaves of many plants in these areas are stems. Other stem succulents can alsobright green, thin and often large. Leaf produce short-lived leaves during the briefsurfaces have large numbers of stomata, rainy season. In leaf succulents, the leaves areonly a single layer of protective cells and swollen and often globular or tubular so as tothe wax coating is thin. Many of these minimise surface area. In plants such asplants shed their leaves in winter in Portulacaria afra, crassulas and peperomias,response to low temperature. both the leaves and stems are succulent. There are also root succulents and plants withIn gardens, plants with these characteristics combined stem and root succulence.must be continually watered during dry Succulents and cacti are about 95% water.weather if they are to survive. Wherever in They can lose up to 70% of this waterAustralia there are severe restrictions on the without damage.use of water in gardens, and you cannot storeenough in tanks, they have no place. When Cacti and other succulents have shallow rootthey die, or you decide to remove them, systems so that they can gain most benefitwelcome the opportunity to plant some of the from the occasional rains falling in theirmany spectacular plants that are more desert habitats. These shallow roots also allowdrought-tolerant. the plants to use the often heavy dews of8 GOOD GARDENS WITH LESS WATER
  • 18. Plants of extreme deserts (from top): Echinopsisdeserticola cactus in the Atacama (Photo: EleanorHandreck); 1500-year-old Welwitschia mirabilis inNamibia.deserts and the water delivered by the coastalfogs of Namibia and the Atacama.In gardens, once established, these plantsneed no water above that provided by rain.The soil must have excellent drainage, withno organic mulch. They may die if you get avery wet year. Plants from less extreme, but still dry, climates (from top): baobabs (Adansonia grandidieri) nearClimatic zones with slightly more rain Morondava, Madagascar, Crassula rupestris andbut still high evaporation rate Mesembryanthemum, from the Karoo andAnnual rainfall in these zones might range Namaqualand, South Africa, respectively.from 100–450 mm, but annual evaporation is extreme deserts. Another adaptation is tooften in the 2000 to 3000 mm range. The disappear underground as bulbs or tubersplants have several types of adaptation to during the dry season.these slightly less extreme climates.Succulence is one, but leaves tend to be larger The major adaptation to high evaporationand less juicy than is common for plants of rate is that leaves are small, even microscopic, 2 – PLANTS AND WATER 9
  • 19. often vertically oriented, with high oil In some areas, such as the western slopes ofcontent, thickened, often rather woody, and Madagascar, the native trees lose all theirwith surfaces protected by several layers of leaves at the start of the long dry season. Ofcells that have thick waxy coatings or a dense course, growth is non-existent during drycovering of short hairs. The harsher the periods and slow when water is in shortenvironment, the smaller and more woody supply, but can be rapid after drought-are the leaves, and the lower their chlorophyll breaking rains. Many of the plants of inlandcontent. The reflective grey colour of leaf Australia have several of the abovesurface coatings reduces leaf heating and adaptations.water loss. Stomata are often sunken into the In gardens, plants with these types ofleaf surface so as to further reduce water loss. adaptations to water shortage will generallyPlants of these areas are superbly attuned to grow well with no or minimal amounts offinding water. An extensive network of near- extra water. But if you plant them moresurface roots make the most of rain when it densely than they would occur in theirdoes fall, but another vertical network natural environment, and especially if youextends 10–20 m, even to 50 m, to reach include trees that become large, you willunderground water. The grasses and other inevitably need to supply more water than isstrappy-leaf plants (such as Dianella, Lomandra delivered by rain. Note also that most of theseand Spinifex (Triodia)) of these dry areas are plants need direct sunshine to flower well.perennials with very extensive root systems.Access to water is enhanced by the widespacings between the plants which win thecompetition for limited water. Some plants Mediterranean-type climatic zonesrelease chemicals from their roots or leaves These areas are in the far south of Souththat prevent other plants from growing near Africa, coastal central Chile, southernthem. Many of these plants shed their oldest California, southern Australia, and all aroundleaves as a last-resort response to extreme the Mediterranean Sea. Rain falls mainly inwater shortage. the winter–spring period, and summers are long, hot and dry. Annual rainfall was around 500 mm, but is now less, and annual evaporation around 2000 mm. Plants have evolved to cope with long dry periods. Most of the plant characteristics described in the previous section apply to these plants too. Note that plants from higher altitudes in these areas will usually be less tolerant of dry conditions than those from lower altitudes.Thryptomene maisonneuvii; tough and showy. (Photo: Plants from these areas are well suited to theEleanor Handreck) gardens of southern Australia. Many grow10 GOOD GARDENS WITH LESS WATER
  • 20. A dryland plant from seasonally cold areas: juniper. Actinostrobus, Widdringtonia) evolved in drier areas and are generally fairly to highly drought-tolerant. Some roses come from these climatic zones and are reasonably drought-tolerant.Dryland plants from southern Africa (from top): Proteaexemia, Leucospermum gerrardii. In gardens, quite a few of these plants manage on rain only so long as they are not planted too closely. But all will benefit fromwell without extra water after establishment, some extra water during the dry season.but they also respond to modest amounts ofextra water during the summer. But note theinformation in the box later in this chapterabout the potential of some of them to Adaptation to cold, wet areasbecome weeds. A main adaptation of plants to the cold, often wet soils of high latitudes, and of the higher elevations of mountains closer to the equator,Zones with dry climates, sometimes is to be low-growing. Plants from these areascold, sometimes hot are suited only to gardens in cold, high- rainfall areas.Many, but by no means all conifers (e.g.cypress, juniper, pine) evolved in areas that As rainfall in southern Australia is likely tohave a combination of cold winters, relatively further decrease, it would be wise to chooselow rainfall and long dry periods. Those with plants that come from somewhat drier areasgrey foliage have the greatest tolerance to than that of your garden, unless of course youdrought. Other conifers (e.g. Callitris, are able to supplement rain with tank water 2 – PLANTS AND WATER 11
  • 21. Table 1. Rough guide to the drought tolerance of different types of plants Plant characteristics Tolerance to drought Large leaves; thin leaves; native to northern Europe, northern North America, Minimal southern South America or the wet tropics Somewhat smaller leaves; from high altitudes in wet tropics or cool climates Slight Smaller leaves; leaves hairy, or grey, or hard, especially if they come from Probably moderately tolerant relatively dry areas Plants with fairly thick leaves; plants whose roots penetrate deeply into the soil; Probably moderately to highly tolerant summer-dormant bulbous plants Small to tiny leaves Usually highly tolerant Plants from inland Australia, including the dry tropics, with tiny, oil-rich leaves Usually highly tolerant and/or hairy and/or grey (waxy) leaves. Plants from similar climatic zones elsewhere in the world Succulents, cacti and other plants from extreme deserts Highly tolerantand greywater (see Chapter 6). If you cannot The top is usually at least partly green andsupply extra water to established plants, the is, in most plants, composed of leaves,plants you grow must be able to survive likely stems, flowers and fruits.dry periods, whether that is two, four or six The bottom part – the roots – is usuallymonths without rain. (See Appendix 1 for hidden away in soil or some other growingsources of information about plants that are medium, such as the organic litter in theknown to be suited to your area.) You are not cleft of a tree.restricted only to succulents, only to Both tops and roots are essential. TheAustralian native plants or only any other decapitated roots of many plants (but notparticular type of plant. of Wisteria and poplar and other plants that ‘sucker’!) soon die; tops alone either grow new roots or they die.The basics of plants and waterThe world of green plants is one of almostinfinite variety. Just stroll through any botanicgardens, arboretum or garden centre to see afew of them. Pick up any book about plantsthat can be grown in gardens to see thousandsmore. Travel in spring through the richness ofthe sandplain flora of Western Australia.Yet within this diversity run some commonthreads: (Almost) every plant has a top and a bottom. One exception are the ‘air plants’ Tillandsia usneoides (Spanish moss) manages without (Tillandsia spp.). roots.12 GOOD GARDENS WITH LESS WATER
  • 22. Some of the many leaf forms (clockwise, from top left): Syngonium, thin, 150 mm; Banksia audax, thick and hard,70 mm; Dryandra tridentata, hard, hairy, 26 mm; Allocasuarina verticillata, less than 1 mm; Lavender, grey, thicklymulched surface, 20 mm; Callistemon ‘Little John’, hard, 38 mm 2 – PLANTS AND WATER 13
  • 23. INVA SIVE GARDEN PL ANTS More than three-quarters of Australia’s weeds produce seeds that stick to clothing and were brought here by botanic gardens, plant animal fur collectors and the nursery trade for use as orna- produce fruits that are attractive to and spread mental plants. Others were imported for use as by birds and animals such as foxes. Red fruits, pasture or crop plants and in forestry. Some weeds as in bridal creeper, are particularly attractive are Australian plants that have escaped from to birds gardens in parts of the country outside their have two or more ways of reproduction (e.g. natural habitats. Others arrived as contaminants seed and bulbs) as in oxalis (soursobs) on imported goods (see www.weeds.org.au for produce seeds that stagger their germination lists of these weeds). over many years (‘hard-seeded’), as in Patter- son’s Curse (Salvation Jane) There is concern that as more gardeners switch to are not eaten by farm or native animals. growing plants that are in tune with their local Unpleasant smell from crushed leaves is often climate, even more plants will become environ- a reason for inedibility, as in bridal creeper mental weeds. Potential weeds have one or more and lantana of the following characteristics. They: have no insect or microbial predators. grow so well in your area without extra water Do not grow plants that are already recognised as that they out-compete other plants weeds, or that have similar characteristics. The can colonise disturbed ground possibility of escape of potential weeds is least if produce huge numbers of seeds, like daisies of you live in a heavily built-up city area, but the all types and orchids such as African Weed- closer you live to bushland, waterways or open orchid or Monadenia (Disa bracteata) countryside, the more careful you must be in your produce seeds that are easily dispersed by choice of plants. In addition, do not dispose of wind or water garden waste by dumping it in bushland, along Not when it (boneseed) out-competes native plants Pretty? in bushland. (Photo: Rachel Melland)14 GOOD GARDENS WITH LESS WATER
  • 24. Bridal creeper is smothering less bushland since the introduction of a fungal biological control agent. roadsides or over the back fence. Rather, put it like to grow. Much more information is into a municipal green organics collection or contained in the fact sheets available at compost it yourself. Use the above list to try to www.weeds.crc.org.au. assess the weed potential of new plants you would The purple peril – Patterson’s Curse (Salvation Jane) Another garden escapee – oxalis (soursob). takes over. (Photo: Tom Morley, DPI, Victoria) All plants have some means of reproducing sunlight so that they can use its energy to themselves, either through spores (ferns) make sugars from the carbon dioxide of the or seeds (other plants). Some also air and from water. This process, called reproduce via offsets. photosynthesis, also releases oxygen back into Roots take water and nutrients for the the atmosphere. The sugars produced by whole plant from the growing medium photosynthesis are the basic building blocks around them. from which the whole plant is made. From them are produced the cellulose, lignin and hemicellulose of cell walls, the proteins of cellLeaves – photosynthetic factories nuclei and seeds, the starches of potatoes andThe leaves are where much of the action of a cereal grains, oils, vitamins, hormones,plant takes place. They are held up towards enzymes, perfumes, flower colours and so on. 2 – PLANTS AND WATER 15
  • 25. growers often enrich the air inside their greenhouses from the current 380 ppm (roughly) carbon dioxide in the air to around 1000–1500 ppm. Do we conclude from this that the increasing concentration of carbon dioxide in the atmosphere from the burning of fossil fuels is going to be good for our plants? Generally no, because plant growth only increases if the plants have an ample supply of all nutrients and are constantly well-watered. The lower rainfall, higherLeaves are plants’ sugar ‘factories’ (Begonia sp.). temperatures and water restrictions resulting from global warming will, in most ofThe ‘factories’ within the leaves where Australia, prevent our plants from using thephotosynthesis takes place are called extra carbon dioxide.chloroplasts. They contain green pigmentscalled chlorophyll. No chlorophyll means nophotosynthesis, no plants on the surface of Plant rootsthe earth, no oxygen in the atmosphere, andhence no insects, birds and animals ‘Out of sight’ should not be ‘out of mind’ as(including us). far as plant roots are concerned. Of course, they are not as pretty as leaves and flowers,Also required for photosynthesis are the but a little study soon shows them to benutrients that are essential to all plants. Water equally fascinating.and nutrients arrive in leaves from the soilthrough roots and stems. Carbon dioxide Have a close look at the roots of the nextarrives through small holes or pores (stomata) weeds that you remove from your garden. Digin the outer, especially lower, surfaces of carefully and gently wash the soil from theleaves. The carbon dioxide diffuses through roots. Note that some weeds have a strong,stomata in much the same way as an odour thick taproot from which thinner rootsmoves from one room to another. radiate into the soil. Others have a multitude of fine roots growing from the base of theInside the stomata, carbon dioxide passes above-ground parts.through cell walls into plant cells that containthe chloroplasts. There, complex reactions, Try to measure the total length of all of thedriven by sunlight and supervised by enzymes roots of one plant. You will give up longand nutrient elements, join carbon dioxide before you get to the 630 km of roots onceand water to form simple organic chemicals. found on a large rye plant. When all the root hairs were included in the total, this onePlant growth rate can increase as the carbon plant had a total root length of 11 000 km!dioxide content of the air increases. Vegetable And that did not include the huge network of16 GOOD GARDENS WITH LESS WATER
  • 26. THREE T YPES OF PHOTOSYNTHESISC3 photosynthesis This is the type of same time. This means that the stomata of thesephotosynthesis used by plants that evolved in plants must open during the day. A down-side oftemperate to cold climatic zones. It also extends this is that water is constantly lost from the opento many plants of Mediterranean climatic zones. stomata.It works well when air temperatures are belowabout 30°C. CAM (crassulacean acid metabolism) Plants that use this method of photosynthesis open theirC4 photosynthesis This type of photosynthesis is stomata at night, when the air is cooler andused by many tropical grasses such as sugar cane, more humid than during the day. Water losscorn, sorghum and the warm-season lawn grasses through them is reduced to a minimum. The(see p. 120), but also by plants such as the salt carbon dioxide that enters at night is convertedbushes (Atriplex, Rhagodia) and Euphorbiaceae. into acids (like the malic acid that gives greenIt is more efficient than C3 photosynthesis at using apples their sharp taste) which are stored untilcarbon dioxide. It is basically an adaptation that the next day. During the day, carbon dioxide isallows plants to thrive under high light, high air released from these acids inside the plant andtemperatures and limited water supply. C4 plants converted to sugars. CAM is used by the manyare better able to cope with drought than are succulents and cacti that are superbly adapted toC3 plants. Recent research has shown that some growing in seasonally very dry environmentsC3 plants also have some chloroplasts that use where day temperatures are high and nightthe C4 method. temperatures often very low. Cacti and succulentsIn both C3 and C4 photosynthesis, light and carbon therefore make excellent plants for gardeningdioxide must both arrive at the chloroplasts at the without extra water. Stem succulent: Pachypodium rosulatum var.C 4 photosynthesis in action: kikuyu lawn. gracilius, Madagascar. 2 – PLANTS AND WATER 17
  • 27. store food, for the plant’s later use (as in carrots) or for the next generation (as in potatoes) store water (as in dahlia and bridal creeper). Size of root systems You would expect that the larger a plant, the more extensive will be its root system. That isMasses of roots are needed to anchor trees against generally true, but there are many variationsrivers swollen by monsoonal rain. on this theme. Most of the roots of the plants we grow in ourmycorrhizal fungus hyphae growing with the gardens are in the top 30–50 cm of soil, butroots (see p. 20). many plants also push roots more deeply ifAll roots: the soil is moist. anchor the plant in the soil. They have to Many trees and shrubs that are adapted to hold it against strong winds and grazing seasonal drought have roots that extract water animals from 10–12 metres below the surface. collect water and mineral nutrients from The widespread spinifex (Triodia spp.) of arid the soil. Australia can send its roots down 50 m.In addition, some roots: The roots of most trees extend horizontally store nutrients, particularly phosphorus, well beyond the ends of their branches. for later use by the whole plant (most Often about 60% of the total root system of perennial plants) large trees is outside the ‘drip circle’. A large tree in a garden can suck water from all of the rest of the garden, making it nearly impossible to grow other plants. It is virtually impossible to have a thriving vegetable garden when the soil is laced with roots from nearby trees. The seedlings of plants from seasonally dry environments produce roots more rapidly and more extensively than those of plants from less harsh environments. This enables them to contact enough water to get them throughPotatoes on sale at their source in Peru. their first dry season.18 GOOD GARDENS WITH LESS WATER
  • 28. Surface roots take up nutrients being recycled from The shallow roots of citrus need to be protected –decaying leaves, and bind the soil. here by weedmat and coarse bark mulch. Drippers are below the weedmat.Roots that grow deep into the soil recycleback to the surface nutrients that have Light to moderate pruning during theleached from the surface in drainage waters. growing season reduces root growth forAn ecologically balanced garden will have at several months. One consequence of this isleast some deep-rooted plants. that young non-dormant trees should not beThe roots of warm-season lawn grasses such pruned at transplanting, as this is a timeas couch and kikuyu can push roots down 2 m when as much root growth as possible isif their tops are not cut too short. In contrast, desirable.the roots of cool-season lawn grasses such as Digging under and near shrubs and treesthe bent grasses penetrate no more than damages their roots and will reduce their30 cm (see p. 121). Even the roots of tall ability to take up water. Never disturb the soilfescue – the most drought-tolerant cool- under shallow-rooted trees such as avocadoesseason grass – barely penetrate to 1 m, and a and citrus.lot less if it is closely mown. Roots need oxygen Roots must have a constant supply of oxygen. Yes, they breathe just as we do. For most plants, this oxygen comes from the air direct to their external surfaces via the pores between soil particles. Oxygen supply will be best when the soil has excellent structure (see p. 34) and when the larger pores are notEucalypt roots, shown exposed in a road cutting, often filled with water. Oxygen moves only veryextend to deeper than 10 m into the soil. slowly through the still water held in the 2 – PLANTS AND WATER 19
  • 29. WHY ARE MYCORRHIZ AL FUNGI USEFUL? Plants have extensive root systems, but these crucifers (cabbage, cauliflower, turnips, systems are enormously extended by the strands of mustard, wallflower, candy tuft, stocks, horse the mycorrhizal fungi that grow from the roots of radish) and the saltbushes. at least 80% of all plants. Many of the toadstools and mushrooms that The spores of these fungi germinate on the can be seen in pine forests are the fruiting outside of young roots, invade root cells, but bodies of mycorrhizal fungi that are living in then live in harmony with their host plant. harmony with the trees. The fungi then grow long strands called Orchid seeds will germinate only when they hyphae out into the soil. Fungal hyphae are are in contact with special types of mycorrhizal very thin, so it takes less energy to grow a fungi. given length of them than it does to grow the same length of root. The plant feeds sugars to the fungi; the fungi increase the supply of nutrients – particularly phosphorus and zinc – and water to the plant in a way that is much more efficient than if the plant did it by growing more roots. The extra water increases the plant’s tolerance of drought and high temperatures. The small proportion of plants that do not form Mycorrhizal fungus growing in association with liaisons with mycorrhizal fungi include the roots.pores of a waterlogged soil. The rates ofmovement of oxygen through air and waterare as different as the speeds of a slow tortoiseand a jet aircraft. Plants that grow in water(e.g. rice, reeds) are able to supply oxygen totheir roots through their leaves and stems.Other facts about rootsOver half of all the organic matter producedduring photosynthesis ends up in the growingmedium, either as dead pieces of roots, or asroot exudates, which are discharges from Reeds being used to purify runoff water at Bau Farmroots. This organic matter provides a rich diet Nursery. (Photo: David Huett, NSW Agriculture)20 GOOD GARDENS WITH LESS WATER
  • 30. do this (e.g. rhododendrons, camellias, many hybrid grevilleas) show symptoms of iron deficiency (yellowing of the youngest leaves) when they are grown in the same soil. Transpiration: the evaporation of soil water through plants One way of thinking of a plant is to imagine it as a bundle of flexible narrow tubes running from root surface to leaf surface. The tubesIron deficiency symptoms in a Grevillea, caused byhigh soil pH. are filled with water. The bottoms of most of these tubes end infor countless millions of micro-organisms that root hairs, which are long cells that protrudeprotect the roots against pathogens, and help profusely from near the tips of growing roots.root growth through the hormones they The top ends of the tubes end in structuresproduce. called stomata. These start to close as the leaf around it gets a bit dry (seen as wilting), orPlant roots take up nutrient elements by when a signal from the bottom end tells itabsorbing them from the water in the soil, that there is not enough water left in the soilwhich is called the soil solution. The actively to fill the tube.growing cells near root tips and in the root-hair zone select the nutrients needed by the When stomata are open, water is evaporatedplant. Bringing the nutrients into the plant through them into the surrounding air. Thisuses oxygen and expends energy. evaporation of water is called transpiration. Transpiration creates a suction in the water-All this is quite easy if there is plenty of each filled tubes inside the plant. This suctionof the nutrients in the soil solution. But draws more water up through the plant andsometimes the concentration of one or more from the soil around its roots in much thenutrients is too low to satisfy the needs of the same way that sucking on a straw raises icedplant. Faced with a shortage, many plants are coffee from a carton.able to modify the soil immediately aroundtheir roots. They exude various chemicals The rate of transpiration increases with anthat are able to dissolve nutrients from soil increase in air temperature and wind speed,minerals. and with a decrease in air humidity. Therefore, plants use water most rapidly onFor example, the roots of plants that evolved hot, windy, dry days. Transpiration keeps theto grow in calcareous or alkaline soils exude plant cool, but it also means that plants mustacid and chelating compounds in response to continue to have access to water if they area shortage of iron. Plants that are not able to to survive. 2 – PLANTS AND WATER 21
  • 31. Path of water through a plant.Temperature and water use them, and they are never short of nutrientsIt is obvious, but has to be stated: as and water. A shortage of water causes stomatatemperature increases, plants lose water more to partly or totally close, so that water lossrapidly. Evaporative cooling is the only way through transpiration is reduced or stopped.they can keep cool. For example, in air with a This also reduces or shuts off the supply ofrelative humidity of 70%, a 5°C rise in leaf carbon dioxide and so reduces or stops thetemperature doubles the transpiration rate. manufacture of the sugars that are essentialThis is particularly important for potted for growth. The more severe the waterplants (see p. 140). deficiency and the longer it lasts, the greater will be the reduction in plant growth. Prolonged lack of evaporative cooling willEffects of water stress on plants cause leaf temperature to rise high enough toPlants grow at their best when the kill leaves.temperature and amount of light are right for Flowering and fruit production are particularly hard hit by lack of water. If you do have to make a choice about where to reduce water use in your garden, don’t skimp on vegetables and fruit trees. Drought causes lettuce and other leafy vegetables to flowerStomata. prematurely, tomatoes to develop blossom22 GOOD GARDENS WITH LESS WATER
  • 32. end rot and cucumbers to become bitter.Fruit trees may drop much of their fruit.Some benefits of water stressWe can use water stress to our advantage inour gardens. Allowing established ornamentalplants to become moderately water stressed isa highly effective way of keeping garden wateruse to a minimum (see below and p. 74).Stress also prevents excessive growth, thus Death eventually follows wilting if more water is notreducing the need for thinning and cutting supplied.back. Disease problems often found in over-wet gardens are reduced. Mild water stress amount of heat reaching the plant. At firstduring the later stages of ripening reduces these plants may wilt only briefly during thefruit size and so improves quality. Rotting of hottest part of the day and will recoversoft fruits is lessened. around sunset, when transpiration is further reduced to below the rate at which water is taken up from the soil. If drying of the soilHow plants deal with a shortage continues, the period of wilting starts earlierof water in the day and lasts longer. Eventually theIf there is plenty of water in the soil, the water point is reached where daytime losses of waterin the largest pores is easily pulled from the cannot be made up at night. Wilting becomessoil by transpiration. But as more water is permanent. The plants begin to wither andremoved from the soil, the remaining water is die. The soil at this point is said to be atheld more and more firmly in progressively ‘permanent wilting point’ (see p. 51 for moresmaller pores, so that it is increasingly difficult information).for the plant to extract water from the soil. The response of drought-tolerant plants isEventually, the plant is unable to extract water different. Their leaves have thick outer cellfast enough from the soil to make up for layers, waxy and hairy coatings, and fewer andtranspiration losses. Stomata close, but there sunken stomata, which together allow them tois still some water being lost from leaf drastically cut water losses when soil watersurfaces. This is a universal response amongst becomes scarce. The hard, woody nature ofplants, but what happens next to the plant their leaves also prevents them from droopingdepends on how drought-tolerant it is. in the manner of drought-sensitive plants. ButThe thin leaves of drought-sensitive plants with a continuing decline in water supply,wilt, curl and hang vertically. These changes they eventually start to lose older leaves as areduce total effective leaf area and hence the means of extending the supply to vital 2 – PLANTS AND WATER 23
  • 33. Fertilisers and water use by plants This book is about water and garden plants. It was tempting to exclude any information about fertilisers, but the fact is that there are close links between the level of nutrient supply to plants, the amount of water they use and the way they respond to drought. Here are some facts (see p. 145 for more information about potted plants, and p. 128 for more information about lawns). Plants such as vegetables and fruit trees that must keep growing vigorously if they are to fulfil their purpose must be fed. This also applies to bedding plants and to perennials such as roses whose blooms are harvested and that are pruned every year. Detailed information is given in Gardening Down-Under (see Appendix 1). The fertiliser situation is quite different for perennial ornamental plants in garden soils.The leaves of this correa looked like this at the end ofsummer, but quickly recovered after the first autumn They need much less than do vegetables, etc.,rains. and usually none once they are established. To get adequate early growth of ornamentalyounger leaves. Towards the end of a dry plants, you will usually need to feed them atsummer, many drought-tolerant plants do planting. Insert a plant pill or about twolook yellowish and droopy, but they get back tablespoons of long-term controlled-releaseto their former glory within a couple of weeks fertiliser into the soil at the bottom of theof rain. planting hole. This initial application should be skipped if the soil has a long history ofBut in addition to these strategies in the fertiliser applications. For most Australianleaves, drought-tolerant plants are also able to native plants and exotics fromcontinue to extract water from soils that have Mediterranean and drier climatic zonesdried to the permanent wilting point of elsewhere, that will probably be all thedrought-sensitive plants. Drought-tolerant fertiliser that is needed (see below forplants are able to use more of the water in a information about phosphorus-sensitivesoil than can drought-sensitive plants (see plants). This applies equally to organic andp. 51 for further information). inorganic fertilisers. The soil itself and24 GOOD GARDENS WITH LESS WATER
  • 34. recycling from fallen leaves will usually However, there are two situations in whichprovide all they need once they are drought-tolerant plants might need someestablished. extra fertiliser after planting. One is if the soil is so deficient in nutrients that the initialYou can easily wreck the superb adaptation application is not enough to produce goodof drought-tolerant plants to low water growth. The other is when you prune thesesupply if you apply more than a small plants and remove the prunings from underamount of fertiliser at planting. Drought- them. You may then need to apply extratolerant plants have evolved to grow on soils fertiliser to replace the nutrients lost in thethat have no more than modest supplies of prunings.nitrogen (from soil microbes andleguminous plants that grow within their You must never apply fertiliser to establishedcommunities), but low to sometimes plants if you cannot supply water to them.extremely low concentrations of phosphorus. Mulches that have been enriched withThe softer, more rapid top growth allowed nutrients should not be used around drought-by repeatedly supplying these plants with tolerant or phosphorus-sensitive plants (seeextra nitrogen and phosphorus will cause box on next page). Restrict their use to fruitthem to use water faster. The fertiliser may trees, vegetables and perennials from whichreduce root growth and reduce or even foliage or flowers are frequently cut.eliminate the growth of mycorrhizal fungion plant roots, so drought tolerance is See the comments on p. 61 about notreduced. It is best to allow these plants to using laundry detergents that containremain hardy by letting them grow at their phosphorus if you want to apply greywater toown natural pace. your garden.Eucalypt seedlings evolved to exploit the phosphorus in ashbeds created by fire. They need a small early supplyin pots and gardens. Left to right: Same nitrogen, increasing phosphorus from zero. But see pp. 61–63 for theeffects of excessive later supply. 2 – PLANTS AND WATER 25
  • 35. PHOSPHORUS SUPPLY If you have any connection with farming, you will allow excessive build-up of phosphorus in your know that farmers have to apply phosphatic soil to the point that it can harm your plants. fertilisers such as superphosphate to ensure Most Australian native plants require moderate adequate crop growth, because most Australian amounts of phosphorus for normal growth. The soils naturally had too little for exotic food crops comments given above about fertiliser use at and pasture plants. Nitrogen is also now widely planting and later apply equally to all of these applied, especially to cereals. While there may be plants. However, there is a group of plants that are a need for some trace elements, it is often nitrogen harmed or killed if they are given the amounts of and phosphorus supply that determines crop yields. phosphorus required by other plants. These are This also applies to most garden soils; it is nitrogen the so-called ‘phosphorus-sensitive’ plants. The and phosphorus that determine the growth of soils of their native habitats have extremely low garden plants. Plant leaves and flowers typically concentrations of phosphorus, so these plants have have phosphorus concentrations that are about evolved mechanisms that are highly efficient at 15% of their nitrogen concentrations. Put another extracting phosphorus from such soils and for way, the ratio of phosphorus (P) to nitrogen (N) in conserving it within their structures. the leaves (the P/N ratio – P concentration divided by the N concentration) will be about 0.15. As a general rule therefore, the fertilisers we use in gardens should also have nitrogen and phosphorus in this ratio. Only where a garden is being estab- lished on non-farmed soil might there be an early need for extra phosphorus. You can easily check the P/N ratio of fertilisers. Take a calculator to the garden centre and do the following calculation. Look on the package for the listing of nutrients. Divide the concentration of total phosphorus by the concentration of total nitrogen (to give the ratio P/N). For example, if a fertiliser contains 15% nitrogen (N) and 2% phosphorus (P), its P/N ratio is 2 ÷ 15 = 0.13. This is about the ratio in which many plants take up these two nutrients. Most fertilisers, notably those based on poultry manure Native vegetation growing on deep sands at Dark and some soluble powders, have much higher Island, South Australia, was decimated by the proportions of phosphorus. Their repeated use will application of phosphorus.26 GOOD GARDENS WITH LESS WATER
  • 36. Any fertiliser applied to these plants must have a P/N ratio of less than 0.1, and preferably less than 0.07. For most gardens, the only fertiliser needed by these plants will be a little urea (N only). A few might benefit from a little extra potash (K), as from potassium sulphate, on very sandy soils. These phosphorus-sensitive plants must not be fertilised with poultry-manure-based products or blood and bone. Nor must they be watered with greywater that contains phosphorus (see p. 61). IfPhosphorus toxicity symptoms in an acacia seedling. you find that in your garden any of the phospho- rus-sensitive plants listed above become yellow,Many species in the Australian proteaceous genera grow poorly or die, the cause is probably largesuch as Banksia, Telopea (waratah), Grevillea, past applications of phosphorus. If this is con-Isopogon, Dryandra, Hakea, and in southern firmed by soil analysis, you will have to growAfrican genera such as Protea, Leucospermum less-sensitive plants.and Leucadendron, are especially efficient at It is essential that you understand that the majorityextracting phosphorus from soils. Application of a of Australia’s native plants are not sensitive tophosphatic fertiliser to soils in which these plants phosphorus. Those from rain forests, both coolare to be grown is a sure way of killing them and tropical, are rarely sensitive. Those in thethrough phosphorus toxicity and/or iron deficien- Myrtaceae family (eucalypts, corymbias, calliste-cy. Death will be surer and more rapid in sandy mons, melaleucas, Leptospermum, Kunzea,soils than in heavier soils. Calytrix, Darwinia, Thryptomene, etc.) are usuallyNon-proteaceous genera known to contain not sensitive. Those from alkaline (high pH) soilsspecies that are prone to phosphorus toxicity are rarely sensitive. All of these non-sensitiveinclude Acacia, Bauera, Beaufortia, Boronia, plants can receive the same early application ofBossiaea, Brachysema, Chorozema, Daviesia, fertiliser as listed above for general ornamentalEutaxia, Hypocalymma, Jacksonia, Lechenaultia plants. But note the remarks about the effect ofand Pultenea. fertilisers on drought tolerance. 2 – PLANTS AND WATER 27
  • 37. Patterns in the soil. (Photo: Eleanor Handreck)
  • 38. KNOW YOUR SOIL KEY POINTS Getting to know your soil Soil texture and soil structure Improving sandy soils When to use gypsumThe main aim of this chapter is to enable you 3. Water – the ‘soil solution’, in whichto maximise the retention of water by your nutrients for plants are dissolved.soil and hence its ability to supply water to 4. Air – which fills the spaces between soilyour plants. The first step is to find out a little particles that are not filled by soilabout what soils are made of. solution.We see in road cuttings, excavation sites andcultivated fields that there is not just oneuniform covering of soil across our planet.Soils in different areas look different fromone another. They have different colours, theway their particles are fitted together isdifferent, and they feel different when we rubthem with our fingers. But despite thesedifferences, all soils have five maincomponents:1. Inorganic particles – minerals that have been produced from rocks by weathering, together with unchanged particles of rock.2. Organic materials – humus, and the dead and decaying parts of plants and soil Natural soils often vary in colour and other properties animals. with depth. 29
  • 39. 5. Living organisms – ranging in size from small animals to viruses.Soils look and feel different because: they have different proportions of the above components the components are grouped together in different ways there are many different types of minerals, and each soil has different proportions of them the mineral fractions of different soils contain widely different proportions of large and small particles.Our look at road cuttings and excavationholes will have shown that the soil changes inappearance with depth. The surface soil –topsoil – usually has a darker colour thanthat below because of the humus(decomposed organic matter) in it. Belowthat – the subsoil – you may see several layersthat differ in colour and/or otherappearance and feel. In many gardens, the‘topsoil’ is in fact not the natural soil of thearea. It is a soil blend that has been producedby a soil supplier and spread over the subsoil. Look closely at the soil of your garden … including itsThe soil in established gardens will have wildlife!been changed over the years throughadditions of mulches, compost poor structure (see below) are harder toand fertilisers. dig than are soils with good structure.) Put the block of soil on a sheet of newspaper.Get to know the soil in your garden 2. Is there a mulch layer on the surface?Go into your garden and dig up a 20 cm deep 3. Is the soil moist or dry? (Areas of drynessblock of soil of spade width and about 5 cm in soil that has recently received rain orthick. irrigation might be due to water repellence.)1. Is the soil easy or hard to dig? (Dry soil is harder to dig than moist soil. Soils with Look at the topsoil.30 GOOD GARDENS WITH LESS WATER
  • 40. 4. Can you see a layer of topsoil above soil limited supply of water. Fine soil over a of different appearance? courser sandy layer will remain saturated5. What differences in appearance can you after rain.) see between the topsoil and the soil 14. Is the whole block just one mass of soil or below it? does its surface have a fine crazing of6. If the topsoil is very different from the fractures that divide it up into small soil below, does the topsoil look like a crumbs that are still held together? (You sandy soil blend from a soil yard? are looking at the structure of the soil,7. Is there any builders’ rubble or other which tells you much about how easily junk between the topsoil and the subsoil? water drains through it and how much water it can hold for plants.)Smell the soil. 15. Can you see any large holes in the soil8. Does it smell pleasantly ‘earthy’ or are that might have been formed by there other smells coming from the soil, earthworms chewing their way through especially the lower part of the block? it? (Sour smells often indicate poor drainage.) Gently poke the soil with a knife or piece of stick.Look closely at exposed surfaces of the blockof soil. 16. Is it easy or difficult to break apart? 17. Does the topsoil behave differently from9. Can you see any differences in the that below it? (Topsoils with ample appearance of the soil other than colour? amounts of organic matter will be more (You may be seeing differences in soil friable than the subsoil below. But some texture or soil structure.) topsoils form crusts that impede water10. Has the block already fallen apart, or is it movement into the soil. See Chapter 5.) still more-or-less in one piece? (Falling apart might mean that the soil is sandy or Now take a couple of tablespoons of topsoil. that it has a loose, friable structure.) Place the soil in the palm of one hand and11. Are roots visible in all surfaces? rub some of it between a finger and thumb of12. Can you see any other layers of soil as you the other hand. go down the block? (Layers might have 18. Is it easy or difficult to break up the clods been formed naturally, but more often in and crumbs? (Hard clods could mean gardens they have been produced during that the soil is ‘sodic’ and so in need of an cleaning up after building or by an application of gypsum to increase its incompetent landscaper.) ability to hold and supply water to plants.)13. If there are layers, do they look quite dense (compacted) or are they loose? (A Now determine the texture of your topsoil. compacted layer could mean that water Soil texture is about the sizes of particles in and roots are not able to penetrate the soil, and the proportions in which they are deeply into the soil, so plants have only a present. You determine texture by working the 3 – KNOW YOUR SOIL 31
  • 41. HOW TO DE TER MINE SOIL TE X TURE Moisten some of your soil in your hand with a Form the moist soil into a ribbon by squeezing it little water. between fingers and thumb. Note the length of the ribbon that you can form before it breaks apart. 1. Does the water instantly wet the soil or does it sit on the surface until you start mixing the Use Table 2 to interpret what you have felt and two? (Water repellence in soils calls for seen. correction by you.) Knead the moist soil with fingers and thumb. As you knead it, add more water as needed to keep it moist, but not sloppy. 2. After a minute or two of working, does the soil still feel and sound gritty or does it now all feel smooth? (Grittiness indicates that the soil contains sand. Absence of grittiness indicates that all particles are smaller than sand size.) 3. Does it feel sticky and slippery? (If so, the soil has a high clay content.) 4. Does it have a silky feel? (A silky-smooth feel shows that the soil contains many particles of silt size.) 5. If the soil dries out a little during kneading, does it become very tough to work, or does it just fall apart? (Toughness indicates a high clay content and possibly a need for gypsum. Contrasting soil texture (from top): loam, heavy clay. Falling apart indicates a high sand content.) (Photos: Eleanor Handreck) Table 2. Main soil textural grades Soil response to kneading and ribbon formation Soil texture Cannot be moulded; single grains stick to fingers Sand Ribbon 6 mm Loamy sand Sand grains can be seen, heard or felt; ribbon 15–25 mm Sandy loam Feels spongy; may feel greasy if much organic matter is present; ribbon about 25 mm Loam Very smooth and silky; ribbon 25 mm Silty clay loam Sand grains can be felt; ribbon 25–40 mm Sandy clay loam Smooth to manipulate; ribbon 40–50 mm Clay loam Sand grains can be felt or heard; ribbon 50–75 mm Sandy clay Feels like plasticine and can be moulded into rods without fracture; ribbons 75 mm or more Medium to heavy clay32 GOOD GARDENS WITH LESS WATER
  • 42. (worked into a soft, plastic condition without air pockets). When wet, they make ideal sealing materials for earth-fill dams. Loams are a mixed bag of soils. From a gardener’s point of view, the best loams drain freely, yet hold plenty of water for plants. They are easy to dig and give good conditions for root growth. Silty loams often set very hard on drying. Crusts that act like prison walls for germinating seeds readily form on the surface of some clay loams. These soils can beIt is to be hoped that the soil compaction causing this improved.ponding is relieved before a topsoil blend is spread.moistened soil in your hand, as described in Clay and humusthe box opposite. Then repeat from Step 18 Clay and humus are the smallest particles ofwith each of the soil layers below the topsoil. soils. Clay and humus particles are so small that 500 of the largest clay particles and 200 000 of the smallest will fit side-by-side onSome soil properties related to soil a line 1 mm long. Smallness means that thetexture surface area of even a small amount of clay or humus can be huge. For example the particlesWater percolates readily through sands, loamy in one cubic centimetre of the finest clay havesands and sandy loams (except those that are a total surface area of about 650 m2.water-repellent). Salts are readily leachedfrom these soils, so plants in these soils can Clay and humus are vitally importantbe irrigated with water that is too salty for use because:on heavier (clay) soils. On the other hand, they control the supply of many nutrientsfertilisers applied to sands are also readily to plantsleached out. Compost and other slow-release they reduce the loss of plant nutrientsfertilisers are very useful for supplying from surface soils into water percolatingnutrients to plants in sandy soils. through the soilClay soils, other than those with an excellent they dominate the ability of a soil tostructure, are generally difficult to dig as they maintain a stable pHcan be sticky when wet and often set hard on they have a major effect on the physicaldrying. Unless they are deeply cracked, water properties of a soil, particularly its abilitypenetration into many clays is slow. In fact to hold and supply water and air and tosome clays are virtually impervious to water if provide a good environment for rootthey are already wet or have been pugged growth. 3 – KNOW YOUR SOIL 33
  • 43. Soil structure Aggregates are ‘glued’ together by organicTexture is an important soil property, but matter, clay particles that are rich in calciumeven more important is the way the particles and secretions from roots and micro-that produce texture are grouped together. organisms. The best way to improve theSoil structure is a term used to describe the structure of a soil is to add organic matter toway the particles of a soil are arranged it. Many clay loams and clays also benefit fromtogether. Good structure is essential if plant an addition of gypsum (which suppliesgrowth is to be excellent. A soil has good calcium). Some sandy soils are improvedstructure if: through the addition of a modest amount of clay (see below). the mineral particles and humus are grouped together into crumbs, or aggregates these aggregates are arranged together so Good things about good structure that there are spaces, called pores, Good structure allows water that falls on the between them soil to soak in quickly. It enables plant roots to the particles that make up each aggregate grow easily through the soil. The roots are are bound together firmly enough so that able to make contact with most of the water the aggregates do not break apart when and nutrients present in the soil. Good rain falls on them or during normal structure also allows ample supplies of oxygen digging from the air to percolate down to roots. It the particles of each aggregate are still prevents waterlogging (see p. 114) by allowing held together loosely enough so that small rapid drainage of excess water. Good roots can penetrate into them to get water structure reduces the effort needed to dig a and nutrients soil compared with that needed for a soil with the aggregates are generally quite small, poor structure. ideally 0.2–3 mm across, rather than larger clods that are quite dense. Poor structure Soils with poor structure tend to have their particles joined together into dense sheets or large clumps. These soils may behave in one or more of the following ways: they will probably be difficult to dig they may be inclined to remain waterlogged for extended periods during the rainy season aggregates at their surface may collapseAggregates are an essential part of good soil structure. during rain or irrigation, with the34 GOOD GARDENS WITH LESS WATER
  • 44. collapsed material forming a dense crust. Such a crust will greatly slow the rate at which water can get into the soil they may break into clods which give a very rough seed bed.Improving the structure of sandsThere is not enough clay present in sands toform aggregates, but they still have astructure produced by the loose packing ofthe grains of sand. But because water is onlystored in the spaces between sand grains, andnot within them as with aggregates, the totalamount of water held for a given depth ofsand is generally less than that held in thesame depth of a loam (see Table 3 on p. 51).So is it sensible to add some clay to sands toincrease their water-holding capacity? Theanswer is generally ‘yes’, especially if the sand Deep roots are essential to survival in the sand plains of south-west Western Australia.is water-repellent. Adding clay is a cheap wayof permanently overcoming water repellence. the water in a large volume of soil and in theThe low water-holding capacity per unit of water table whose surface may be 10–20 mdepth of sands has often been considered a below the surface. They do not have to rely onproblem because frequent application of the small amount of water held in thewater is needed to maintain shallow-rooted uppermost 30 cm, which is all that isplants in them. But the real problem is that accessible to the shallow roots of many otherthe wrong plants are being grown. There are plants.plants that grow very well in deep sandswithout frequent watering. Here is the proof. So if the soil of your garden is a deep sand, the simplest way to have an excellent gardenThe deep sands of low rainfall areas of south- is to grow only those plants that havewestern Western Australia support a huge extensive and deeply penetrating rootnumber of plant species through some of the systems. You will choose plants that growharshest summer droughts in the world. naturally on deep sands in areas of fairlyThese plants thrive in these deep sands low rainfall.because their seedlings rapidly produceextensive root systems that penetrate to as However, you might well choose to modifydeep as 20 m. They therefore gain access to small areas of your sandy-soil garden if you 3 – KNOW YOUR SOIL 35
  • 45. want to grow shallow-rooted plants such asfruit trees, vegetables and herbs.You can convert the top 20 cm of a sand into asandy loam or loam by adding 20–40 kg ofcrushed clay soil per square metre and a10 cm layer of organic matter and thoroughlymixing them together, preferably with arotary hoe. An excellent source of calcium.Improving the structure of clay soilsMany, but not all, soils with high clay contents Extra calcium can be supplied in two ways:are difficult to manage in gardens. Difficult 1. The simplest for gardeners to use isclay soils can be improved by: gypsum (calcium sulphate). Apply 1–2 kg adding large amounts of organic matter per square metre. It may be left on the adding a source of soluble calcium, such as surface or dug in, whichever is easiest. gypsum or calcium nitrate, if testing shows Rain and irrigation will dissolve gypsum that a benefit will be obtained applied to the soil surface and move it (maybe) adding sand. down into the soil. 2. Improvement will be more rapid if you also add one dose of a more soluble source of calcium such as calcium nitrateImproving clay soil structure with or NUTRIsorb Ca9® (available fromsoluble calcium suppliers of specialist products for theIf your soil shows the following signs of poor turf industry) along with the gypsum. Astructure: soluble source of calcium is particularly useful when the amount of water is slippery and sticky when wet, available to leach the sodium displaced tends to slump and get very muddy during by calcium from the topsoil is limited. rain, For calcium nitrate, apply 20–30 g/m2 forms a crust on drying, and water in thoroughly. allows only slow entry of rainwater, does not break into anything smaller than large clods during digging, How to check for a need for extrathen it is likely that application of soluble calciumcalcium to it will improve its structure. (Use Take a sample of the soil in the palm of onethe test below to see whether your soil will hand, add some rainwater or deionised waterbenefit from an application of calcium.) (not tap water, as the salts in it will give a false36 GOOD GARDENS WITH LESS WATER
  • 46. kneaded soil into a cube about 5 mm across. Drop this into a glass of the rainwater or deionised water. Watch what happens over the first hour, and then after 24 hours. Do not disturb the glass during the test. You will see one of the following: some aggregates remain unchanged, evenGypsum response test. Soil cube immediately after after 24 hoursplacing it in the water (left); 24 hours later (right).Cloudiness indicates a need for gypsum. others fall apart within the first hour, but the smaller aggregates so formed remain where they fallresult), and knead the soil until all the lumps others, whether they fall apart or not,have been broken up. Squeeze some of the slowly disperse into the water, first forming HOW CALCIUM WORK S Cloudy water in the test just described indicates nent beneficial effect on soil structure. Its calcium that the proportion of sodium ions relative to exchanges place with sodium on clay particle calcium and magnesium ions on the clay particles surfaces. This also allows the particles to move is too high (technically, the soil is said to be closer together and to remain there. The displaced ‘sodic’). The sodium ions prevent the particles sodium ions move away from the particle surfaces. from coming close to one another. They can be With enough water, they are flushed away into the forced closer, or prevented from separating in the subsoil. One application of gypsum will continue first place, if the concentration of any salt in the to provide calcium for this process for many solution around them is increased. That is exactly months to years. what happens when a sodic soil is irrigated with salty water, including laundry effluent water when Ca K Mg laundry powders are used (see p. 61). However, as Ca Ca Ca soon as water of lower salinity, like rain, falls on Ca Mg K the soil and dilutes or washes away some of the K Ca Ca Ca salts, the full effect of the sodicity soon shows. The Ca Na Mg Ca Ca only salts that give lasting improvement are Ca Ca calcium salts. Ca Ca Ca Gypsum is slightly soluble in water. The salinity so Ca Mg produced is the first step in improving a sodic soil. Cations are held on the surfaces of clay and humus But the calcium of gypsum also has a more perma- particles. 3 – KNOW YOUR SOIL 37
  • 47. a ‘halo’ of clay particles around the improvement in the structure and drainage of aggregate. This halo then spreads to a the soil. The more clay in the soil, the greater general cloudiness throughout the the volume of sand needed to gain water. improvement. The sand and soil must be thoroughly mixed together. This mixing mustExtra calcium will not improve the structure not be done when the clay soil is very wet. Youof a soil whose aggregates remain unchanged will cause serious damage to whateveror that fall apart without dispersion during structure it has if you do this. Wait until attesting. least three days after rain.Calcium will improve any soil that produces Improvement in structure will be greatest ifcloudiness during this test. The greater the you include plenty of organic matter (andcloudiness of the water, and the more rapidly gypsum if testing shows a need) in the topit develops, the greater will be the benefit of 15–20 cm of the new soil. Decomposition ofadding extra calcium to the soil, and the this organic matter by micro-organisms willhigher the amount needed. form humus that will bind the sand and clay into stable aggregates. Growth of plant roots will aid this process. It will take some yearsImproving clay soils with sand for the full benefits to be obtained.You already know that clay soils have lesssand in them than sands and loams, so youmight conclude that just adding some sandto them will make them easier to manage.‘It ain’t necessarily so!’ If you add only asmall amount, say 10% by volume (about15 L per square metre to treat the top 15 cmof the soil), you will almost certainly worsenthe structure of a clay soil. The sand willsimply clog the few spaces that there are inthe clay.Here are some guidelines for those who do This otherwise excellent Santa Ana couch lawn, whichwant to improve a clay soil through the survives Adelaide summers with minimal irrigation, had a small patch that died off each summer. Diggingaddition of sand. showed the cause as the concreted stump of a clothes line that had been left in situ when the lawn had beenIt is only after you have added sand with a established. The grass in this patch had access to avolume of 60–200% of that of the soil being 15 cm deep reservoir of water instead of the moretreated that there will be a noticeable than 2 m (Table 27, p. 123) elsewhere.38 GOOD GARDENS WITH LESS WATER
  • 48. O RG A N I C M AT T ER AND SOILS KEY POINTS Organic matter is a vital component of all soils Organic matter improves soil structure and water-holding capacity Humus explained How to make and use compost A few problems to avoidOrganic matter is a vital part of all healthy How organic matter improves soilsoils. Its main beneficial effects are: structure and water-holding capacity1. Improved soil structure, so that: When you apply compost, cow manure, the soil holds more water for plants poultry litter or a green manure crop to a soil, water readily moves into the soil there is a massive explosion in the population waterlogging is less likely. of microbes in it. These microbes (bacteria,2. A major source of nutrients for plants. fungi, etc.) produce sticky secretions and3. Reduced leaching of plant nutrients from humus which bridge the gaps between the soil. mineral particles or groups of mineral4. To buffer the soil against rapid change in particles and so bind them together into pH. crumbs or aggregates.5. Biological control of disease-causing microbes through the decomposition of Typically, no more than 30% of organic newly added organic materials. Adding materials added to a soil remains after a organic matter is a powerful way to year. The rest has been used as food by control plant root diseases without countless hordes of micro-organisms and has chemicals. ended up as carbon dioxide, water and6. Hormonal effects on plants, especially to nutrient elements that have been released improve root development. into the soil. 39
  • 49. As the years roll by, less and less of the Compostremaining organic matter is able to be used Compost is what is left of dead plants afterby micro-organisms. Some of it is protected they have been placed in bins or heaps andby being sandwiched between clay particles. partly decomposed by microbes. AllMuch of it is humus. This is long-lived and is gardeners can produce some compost forvital for the well-being of your soil and to themselves.future generations of plants that will grow init. Humus is essential to good soil structure Incorporating large amounts of compost intoand the ability of your soil to provide air and the soil is essential when a new garden iswater to the roots of your plants. being created. A 10 cm thick layer mixed into the top 20 cm of soil would not be too much.Tables 3 and 4 (pp. 51 and 52) give examples The need for later additions depends on howof the ability of organic matter to increase a much natural recycling of organic matter issoil’s ability to hold water. Adding organic taking place. Where all leaves and twigsmatter to a soil is a powerful way of falling from shrubs and trees remain undermaximising the retention of rain or irrigation them, no extra compost may be needed. Butwater in the soil. where leaves are removed, topdressing with compost every few years is desirable. Where the soil is used to grow vegetables, it isHumus essential that compost be added to the soil atHumus is the more-or-less stable part of soil least annually.organic matter remaining from thedecomposition of plant and animal remains.It is dark-coloured and consists of large Commercially produced compostorganic molecules containing mainly carbon, Commercially produced compost can behydrogen and oxygen. These molecules are bought from garden centres and landscapingstabilised by aluminium. They also contain supply yards. These composts have beenconsiderable amounts of nitrogen, sulphur produced from the green organics that areand phosphorus, and smaller amounts of now universally collected in our cities andother elements. Most humus is probably towns for recycling. Compost that conformsformed from lignin, the material that gives with the provisions of the Australianwood and plant stems their rigidity. Standard for Composts, Soil Conditioners and Mulches is guaranteed to be free of weed seeds, pathogens, toxicity and harmful levelsIncreasing the organic matter content of of heavy metals, and to have minimal levels ofyour soil contamination and nitrogen drawdown. TheThe two simplest ways of increasing the organic package will give information about its rate ofmatter content of your soil are by leaving all use so that plants are not harmed by itsfallen sticks and leaves on the soil surface to rot salinity. Compost that does not indicatedown naturally, and by applying compost. conformity with the Australian Standard may40 GOOD GARDENS WITH LESS WATER
  • 50. you want acidic compost for putting around acid-loving plants, or if the pH of your soil is already at 6.5 or higher. 5. After about six months you will be able to remove compost from the base of the bin, either through the door, if your bin has one, or through the opening created by raising the bin vertically by 10–20 cm. 6. Larger families may need to use two bins. The contents of the first bin should have rotted down to compost by the time youTurning a green organics windrow at Jeffries have filled the second bin.Landscape Suppliers, Buckland Park, South Australia. 7. You can speed up the composting by adding earthworms to the materials.be OK, but it may not be. Note that some They will probably come in naturally if(non-Standard) composts produced from the the bin sits on soil, but otherwise you canmanure of feedlot cattle have such high levels get some from a friend’s compost bin orof zinc (700–1000 mg/kg) that their repeated buy compost worms from a gardenuse over some years can cause zinc toxicity to centre.plants growing in acidic soils. Poultry manureproducts have much lower zinc Because the materials in a compost bin doconcentrations. not get hot enough to kill pathogens and weed seeds, do not add diseased plants and any with viable seeds on them to these bins. Put these materials in the green organicsHome-made compost recycling bin so that the heat generatedAll you need to do is to drop the materials tobe composted into a bin. You will haveuseable compost in six to nine months.1. Buy a plastic compost bin.2. Sit it on the soil (preferably), paving blocks or an area of concrete in a part of your garden that is easy to get to without getting your shoes dirty.3. Lift the lid and tip your kitchen scraps, lawn clippings, weeds and moistened autumn leaves into it.4. Continue until the bin is full. Occasionally lightly sprinkle garden lime Two of the many types of domestic compost bins that onto the materials, but don’t do this if are sold at hardware stores. 4 – ORGANIC MATTER AND SOILS 41
  • 51. during commercial composting (60–70°C) Mulch or dig in?will pasteurise them. There is no point trying to dig organic materials into the soil under trees and shrubs. You will damage too many roots. Spread theOther organic materials compost on the soil surface and top it with aMany different types of organic materials are coarse mulch (see p. 100). Microbes andavailable in garden centres and hardware earthworms will do the rest for you.stores. Here is comment on a couple of them. You can dig compost into the soil of aPelleted poultry manures have quite high vegetable patch.concentrations of soluble nutrients, so do not Organic gardeners might also make a surfaceuse them at higher than the rates application of compost between rows ofrecommended on packages, which is usually vegetables part-way through a growing season.not more than 300 g per square metre. Youcould repeat the application after a month orso if your plants need more feeding. The highphosphorus content of poultry manures Possible problems caused by organicmeans that you must not apply them to matterphosphorus-sensitive plants (see p. 26). While adding organic materials to your soil is overwhelmingly beneficial to that soil and toMost products labelled as mushroom your plants, there are a few problems thatcomposts are the spent composts removed need to be avoided.from mushroom farms after a mushroomcrop has been harvested. The material Use of diseased plant materials can spreadcontains both the compost and the ‘casing’ disease to your garden. That is whyonto which the mushroom spore was composts are the safest materials to use forsprinkled. Mushroom composts themselves providing extra organic matter to yourare usually of neutral pH, but casings are very soil.alkaline, so spent mushroom composts are Some fresh plant materials contain naturalusually alkaline. Their high nutrient content chemicals that are toxic to the roots ofoften makes them very salty. Do not use such young plants. Composting eliminates thesecomposts if your soil is acid and you want to toxins.keep it that way. Use them much more Woody materials have very lowsparingly than you would use ‘ordinary’ concentrations of nitrogen. If you digcomposts. them into a soil, the microbes that decompose them will use soluble nitrogenNote the comments on p. 24 about the in the soil and so decrease supply to youradverse effects of fertilisers, both organic and plants. The coarsest of these materials caninorganic, on plants’ drought tolerance. be used as mulches, but the finest (e.g.42 GOOD GARDENS WITH LESS WATER
  • 52. sawdust) need to be composted before use the soil water-repellent. This is less likely,in the garden. but not impossible, with clay soils. DealRepeated heavy additions of organic with water repellence as shown inmaterials to sandy soils will tend to make Chapter 5. 4 – ORGANIC MATTER AND SOILS 43
  • 53. Growing in the reservoir.
  • 54. YOUR SOIL IS A R ESERVOIR KEY POINTS Soils are reservoirs of water for plants Deep roots = access to more water Maximising water entry into your soil Using organic matter to increase the amount of water held in your soilMost of the water that flows from our taps and through its leaky bottom and by evaporationshowers comes from a reservoir that stores from its surface. The length of time it canrainwater. Reservoirs are mainly lakes that supply our plants depends on:have been created by placing a wall across a Its size. Reservoir size increases as thestream or river. The other main type of depth of soil wetted by rain or irrigationreservoir is a natural underground store water increases. But as far as our plantscalled an aquifer, from which water is pumpedvia a borehole. This water too was once rainthat percolated down through the soil.Some facts about reservoirs are: The larger the reservoir, the longer will it be able to supply water, if it starts off full. The faster the rate of removal of water, the shorter the time until it runs dry. The higher the rainfall in the catchment area of a surface reservoir, the faster will be its filling.The soil of your garden is a reservoir thatstores water for your plants. It is filled byprolonged rain or irrigation. It is emptiedmainly by plants, but also by losing water Reservoirs hold water for our use. 45
  • 55. The tiny spaces (capillaries) between particles in thisThe deeper roots penetrate into a moist soil, the larger soil aggregate quickly attract water. The arrowis the reservoir of water that is available to the plant. indicates the border between dry and wetted soil. are concerned, the effective maximum How water is held in soil size of the reservoir is the volume of soil If we turn a cup of water upside down, all the into which their roots grow. A plant water runs out, pulled out by the force of whose roots penetrate one metre into gravity. The top part of a soil is a bit like an moist soil has access to about double the upturned cup; it doesn’t have a leak-proof amount of water contacted by a plant bottom to it. Why is it that all the water in it whose roots penetrate to only half doesn’t just run out into the deep subsoil? a metre. The answer is that soil particles and water Type of soil. Different soils have very usually like to stick together; water is different abilities to hold water (Table 3). attracted to the surfaces of soil particles and Not only does the total amount of water is held fairly firmly by them. held vary, so also does the availability of This attraction can be seen if you touch a that water to plants. Adding organic small clod of dry soil to water sitting on a matter to a soil usually increases its plate: the water is rapidly pulled – soaked – ability to hold water (Tables 3 and 4, into the soil. Attraction can also be seen when pp. 51 and 52). we stand a pot of dry garden soil in a shallow Rate of removal by plants. Obviously, the tray of water. The surface of the soil will be greater the rate of removal, the shorter wet within a few hours because the attraction will be the time until the reservoir between soil particles and water pulls water dries up. up against the downward pull of gravity. Mulch quality. Water evaporating from the soil surface is lost from the reach of our The total ‘amount’ of attraction per cubic plants. This loss can be minimised by metre of soil will be greatest for soils with the covering the soil surface with a blanket of greatest total particle surface area. That an effective mulch (see Chapter 9). means that clay soils, with their huge numbers46 GOOD GARDENS WITH LESS WATER
  • 56. range can be from more than 100 mm (depth of water) per hour to less than 5 mm/hr. It could be less than 1 mm/hr for a heavily compacted clay soil. The optimum range is roughly 10–25 mm/hr. Here is what happens when rain falls onto a soil. Some water enters the soil and fairly quickly flows down through any large holes, such as cracks, worm burrows and old root channels. Some of the water soaks out from these large holes into the surrounding soil. Other water slowly soaks down from the surface through smaller channels between the large holes.A wetting front moving down through dry soil. Infiltration of water will be slow if there areof small particles and therefore large total few or no large holes. It will be especially slowparticle surface area, have a greater total if the aggregates of the soil surface fall apart‘pull’ on water than does the same amount of and clog the channels.a sandy soil. Table 3 gives a rough idea of theamounts of water that can be held in soils ofdifferent textures. How to increase the water infiltration rate of your soil The rate of infiltration of water into a soil isGetting water into soils increased as follows.It is absolutely essential that the rain or Overcome crusting and prevent crustirrigation water that you do have produces formation:the maximum benefit to your plants. That – Protect the soil surface with mulch andmeans that as much of it as possible must soak ground cover plants.into your soil. – Apply gypsum, if testing has shown itIt is of course impossible for any soil to soak to be useful. Maintain good soil structure and improveup all of the water in a deluge from a poor structure:thunderstorm or a tropical downpour. Much – Maintain or increase the organicof the water of light showers falling onto matter content of your soil.already very wet soil may not soak in. – Prevent compaction of surface soil.The rate at which water soaks into soil – the That means avoiding, as much asinfiltration rate of the soil – is usually highest possible, walking over wet soils. Suchfor sands and least for heavy clay soils. The walking compacts the soil by collapsing 5 – YOUR SOIL IS A RESERVOIR 47
  • 57. Ground cover plants such as this Portulacaintraterranea protect the soil, and also look attractive.(Photo: Eleanor Handreck) pores between aggregates, decreases the porosity of a soil, and so reduces the Layers of different types of soil are often created infiltration rate. Compaction will be during building and landscaping operations. Some can reduce movement of water into the soil. greatest during the first couple of days after rain or irrigation, and becomes less as the soil dries out. consider starting again after you have – Don’t dig the soil when it is very wet. broken up the whole of the compacted Wait for one to two days after rain or layer of soil. For a longer-established irrigation. Digging is easiest after the area, you need to punch a large number soil has drained for this time. of holes through the compacted soil Mix any layers of soil of different texture: with a crowbar or auger. Dig 30 cm deep holes into the soil at a – A layer of coarse sand underlying soil of number of places around your garden, or finer texture, which will act as an at least where water ponds during anti-drainage layer. This is because the prolonged rain. Look closely for any of the suction exerted on water by the fine soil following: is greater than that exerted by the – A layer of heavy clay that has been coarse sand. Water will not pass into compacted by construction machinery this coarse sand until the soil above it is or soil that has been stuck together with saturated. The soil above it will remain cement residues. Such a layer may wet enough after drainage into the sand totally stop root growth through it. The has stopped to cause damage to plants depth of the reservoir available to your that need good drainage. Buried layers plants will then be only that of the of coarse sand are usually not natural, surface soil above the compacted layer. but have been put there by uncaring If the garden is new, you should builders and left there by incompetent48 GOOD GARDENS WITH LESS WATER
  • 58. landscapers. Mixing the coarse layer Improving wettability into the soil above and below it will There are two ways of improving the overcome the problems. wettability of non-wetting soils. Reduce slope through terracing: – The steeper a slope, the more likely is it 1. Add clay: Non-wetting of sandy soils can that rain will run off before it can soak usually be permanently cured by into the soil. Any slope that is steeper increasing their clay content to above than about 5% (1 m drop in 20 m about 8%. The amount of clay to be horizontal distance) should be added depends on the depth of sand to terraced. Remove the topsoil before be treated. For 10 cm depth, add terracing and spread it back over the 10–20 kg clay soil to each square metre. top of the subsoil behind the retaining For 20 cm depth, add 30–40 kg/m2. walls. Mix sand and clay very thoroughly, Overcome water repellence in sandy soils. preferably with a rotary hoe. This action should eliminate the need to use wetting agents.Water-repellent (non-wetting) soils 2. Use wetting agents: A wetting agent isMany very sandy soils are naturally somewhat really just a special type of detergent thatwater-repellent. Other sandy soils can become is only slowly biodegraded and is notwater-repellent following the addition of large toxic to plants at the recommended rateamounts of organic matter. Water can sit in of use. The wetting agent allows water topools on the surface of the dry soil or channel spread more easily across the surfaces ofdown in only a few places. Difficulty in particles in a soil, in much the same waywetting is caused by the presence of waxy that soap or detergent allows water tomaterials on the surfaces of sand particles. spread over and stick to a greasy plate. AllThese waxy materials are produced mainly by wetting agents are eventuallyfungi as they decompose organic matter. biodegraded. After three to six months, more may need to be applied. Despite what advertisements say, wetting agents are usually needed only on sandy soils. They are unlikely to improve the wetting of clay soils, unless these have been made water- repellent through very heavy applications of organic materials.If a few drops of water take longer than about a How to apply wetting agents to sandyminute to soak into soil that has been thoroughlydried in the sun, the soil should be treated to soilsovercome its water repellence. 1. Use a fork to make small holes in the soil. 5 – YOUR SOIL IS A RESERVOIR 49
  • 59. 2. Apply wetting agent as per the label, but fairly dry before the rain, and that the plants typically at 5 mL of concentrated wetting growing in it would have needed watering agent per square metre. You must dilute within a couple of days. the concentrated wetting agent so that Let us further suppose that all of the rain has the 5 mL is carried in about 2 L of water. soaked into the soil. While some has gone a Thus, 25 mL of wetting agent in 10 L of long way down worm burrows, the average water will treat 5 m2 of soil. Use a depth that is now moist will be something like watering can. Alternatively, apply a 0.7 m for a clay and up to 1.4 m for a sand. It granular form of wetting agent at the will have taken no more than a few hours for recommended rate. the water to finish draining down through3. Encourage penetration of the solution by the sand. Drainage down into a clay soil further forking, if necessary. would have taken many days.4. Then apply water at a low rate (5–10 mm per hour) so that water can penetrate deeply into the soil. If you cannot use sprinklers, apply the wetting agent (either Field capacity liquid or solid) during rain or just before When the main drainage of water down it looks like raining. into a soil has finished, that soil (or rather, that part of it that is now moist) is said to beBecause all effective wetting agents are toxic at ‘field capacity’. The reservoir is full toto plants if applied at higher rates than that depth.recommended, do not use gadgets that applywetting agents every time you water. The soil is able to hold approximately this amount of water for long periods if evaporation from its surface, and transpiration by plants, is prevented. In a soilWater in soils at field capacity, water has drained from theIf we are thirsty, we can drink a glass of water, largest pores, but all small and manyright to the very bottom. Plants are not so medium-sized pores are filled with water. Youfortunate. They cannot completely drain the can get an idea of what happens from the wayreservoir of their soil, even if they are short of that cooking water drains from the largerwater. This section gives information about spaces between peas but some water is left inthe size of the reservoir in different soils and the smaller spaces where the peas touch onethe proportion of that water that can be used another.by plants. It follows from this that a given depth ofLet us suppose that steady rain has delivered a soil with many small and few large pores100 mm of rain to your soil. That means that, (clay) will hold more water than will theif the water were all sitting on the surface, it same depth of a soil with few small andwould cover the soil to a depth of exactly many large pores (sand), as shown in100 mm. We will assume that the soil was Table 3.50 GOOD GARDENS WITH LESS WATER
  • 60. Table 3. Approximate amounts of water held in soils of different textures Number of mm of water per cm depth of soil Needed to wet the soil to Remaining at the Soil texture field capacity Available water* permanent wilting point* Sand 0.9 0.7 0.2 Loamy sand 1.4 1.0 0.4 Sandy loam 2.3 1.4 0.9 Sandy loam plus organic matter 2.9 1.9 1.0 Loam 3.4 2.2 1.0 Clay loam 3.0 1.4 1.6 Clay 3.8 1.4 2.4 Well-structured clay 5.0 2.0 3.0 * See the box below for a discussion of what these terms mean.Enlarging the reservoir: how to increase AVAIL ABLE WATER ANDthe water-supplying ability of your soil PER M ANENT WILTING P OINTThe most effective way of increasing the In Chapter 2 it was stated that when drought-ability of your soil to supply water is to sensitive plants wilt permanently, the soil inimprove its structure (see above and Chapter which they are growing is said to be at the3). In particular, water must move quickly ‘permanent wilting point’. There is still someinto the topsoil and there must be no water left in the soil, but these plants cannot usebarriers, such as a compacted layer, to water it. The difference between the amount of waterpenetration into the subsoil. Organic matter held in the soil at field capacity and at theis a key to excellent structure and deep water permanent wilting point is the amount of waterpenetration. The combination of deep water that these plants can use. This amount is referredpenetration and plants that have the ability to to as the ‘available water’ content of the soil.send their roots deeply into the soil (see Table 3 shows that loams and some well-struc-p. 18) is the most powerful way you have of tured clays hold the largest amounts of availablemaximising the size of the reservoir in your water. Note how adding organic matter to asoil. Why waste all that lovely water by sandy loam, or improving the structure of a clay,growing shallow-rooted plants? increases the amount of available water that can be held.There are many products that claim variously In contrast to this response by drought-sensitiveto save water, reduce water use, decrease plants, drought-tolerant plants are able to extractwatering frequency and so on. These claims some of the water that remains in a soil atare rarely supported by the results of permanent wilting point. The amount of waterindependent testing. They often appear to be available to them is therefore higher than thelittle more than marketing hype. The available water contents listed in Table 3, but notinformation provided in this book about how as high as the total amount held at field capacity.soils store water and how plants use water will 5 – YOUR SOIL IS A RESERVOIR 51
  • 61. Table 4. Effect of decayed manure on the available water content of sandy soils(From: Bouyoucos, GJ (1939). Effect of organic matter on the water-holding capacity and the wilting point of mineral soils. Soil Science47, 377–383) Manure addition rate (cm depth Sand (mm available water per cm Sandy loam (mm available water per mixed into top 20 cm of soil) depth of soil) cm depth of soil) 0 1.2 1.6 5 1.7 2.0 10 1.9 2.2enable you to assess these claims of large gives an example for a product that iswater savings. currently on the market. The maximum amount of water held when water crystals are incorporated into soils isEffect of organic matter on available usually rather less than 100 g/g, because ofwater the combined effects of salts, includingTable 3 contains one example of the ability of fertilisers, and physical constraints on theorganic matter to increase the available water swelling of the crystals in the soil. Researchcontent of a soil. Table 4 gives more examples. results for currently available products reportYou can see that modest additions of organic amounts of about 50 g/g. Repeated cycles ofmatter increased the available water content wetting and drying gradually reduce theof these light-textured soils by about 50%. amount of water held by the crystals to zero after some years.How useful are water crystals? Availability to plants of the water heldWater crystals are synthetic plastic materials Not all the water held by water crystals can bethat absorb many times their weight of water. used by plants. Theoretically they should beMost of those currently on the market are 275cross-linked acrylamide/acrylic acid co- 250polymers with ammonium and/or potassium. 225Water crystals are sold for use in potting Water held (g/dry g)mixes and soils as a means of increasing water 200supply to plants. Here are some facts. 175 150Effect of salinity 125The amount of water these products absorb 100depends on the salinity of that water. It can 75 0 200 400 600 800 1000 1200 1400 1600 1800 2000range from about 300 grams per gram (g/g) Salinity of water (µS/cm)of dry crystals for very pure water to only a The amount of water held by water crystals decreasesfraction of this at high salinity. The graph markedly as salinity increases.52 GOOD GARDENS WITH LESS WATER
  • 62. COMPARISON OF SE VER AL WATER- HOLDING M ATERIAL S The data in Table 4 show that mixing a 10 cm layer of manure into the top 20 cm of a sandy loam soil increased its available water content by 0.6 mm/cm (2.2 – 1.6). Further additions are likely to be needed to maintain this effect overOne quarter of a teaspoon of water crystals beforeand after absorbing deionised water. the years. Coir fibre dust (e.g. Cocopeat) holds aboutable to use 95% of it, but research results 0.6 kg plant-available water per litre of expandedsuggest that it could be no more than half the material. A 10% by volume addition to the toptotal held by the crystals, or as little as 25 g/g. 20 cm of one square metre of a sandy loam willDespite these limitations, there is solid require 20 L of the coir. This amount will holdresearch and practical evidence that the water about 12 kg (= L) of available water (= 12 mmcrystals currently available are useful in two depth of water if it were spread over 1 m2). Thisways in garden soils: addition will therefore increase the available water content of the sand by 12 ÷ 20 = 0.6 mm/1. When planting trees and shrubs, survival cm depth of soil. The coir will gradually decom- rate and early growth will often be pose over several years, so the amount of extra improved when you include a slurry of water held will gradually decline. water crystals in the planting hole (see p. 110 for details). What is the effect of mixing 100 g (dry)/m22. If your soil is very sandy, including water water crystals into the top 20 cm to the same crystals will allow the sand to hold more sandy loam? If we assume that the crystals hold water and so extend the time until the 40 g plant-available water/dry g, the total plants must receive water again. Research amount of plant-available water held will be results show that maximum benefit is 100 × 40 = 4000 g/m2. This is 4 L of water/m2, obtained when the addition rate is in the which is equivalent to a depth of 4 mm water. range 100–300 g (dry) crystals per square This is 4 ÷ 20 = 0.2 mm water/cm depth of soil. metre, incorporated into the top 20 cm It would be necessary to treble the addition rate of soil. (to about 300 g/m2) to achieve a similar increase in available water supply to that given by coir orWater crystals, and indeed any other means of compost incorporated at the rates listed above.increasing the water-holding capacity of a soil,do not reduce the amount of water used by your Readers are left to decide which option will beplants. In fact, your plants will use more water if best for their situation.the amendment allows them to grow bigger. 5 – YOUR SOIL IS A RESERVOIR 53
  • 63. Ultimate salinity.
  • 64. WAT ER Q UA L I T Y KEY POINTS How to check the quality of your water supply Interpreting salinity readings Easy interpretation of water analysis information Minimising the effects of salinity on plants and soils Greywater: all the facts How to divert and use greywater without problemsMost water has various things dissolved in it. supplies are sodium and chloride (as inEven rainwater direct from the sky has a low common salt), calcium, magnesium,concentration of salts from sea spray bicarbonate, sulphate and phosphate.(common salt), lightning (nitrates),pollution and dust. This rain will pick upmore salts (from bird droppings and leaves) How do I know if my water is salty?as it flows from roof to tank. When rain flowsover and through soils to reach streams and The simplest way of finding the saltiness ofreservoirs, it dissolves more salts from the your water is to ring your water supplysoils. In dry areas, more salts can enter authority or look up the information on theirstreams from saline springs and seepage from website. You will get a figure for the electricalirrigated crops. Greywater has extra salts conductivity (EC) of the water they supply tofrom detergents. Low concentrations of salts your area. The higher an EC reading, thein water do not harm our plants and soils, but saltier the water. EC readings internationallyas salt concentration increases, the possibility and for all Australian states except Westernof harm being done also increases. Australia are given in units called microSiemens per centimetre (µS/cm) orThe simplest way of describing the salts in deciSiemens per metre (dS/m). Onewaters is by listing their separate parts – dS/m = 1000 µS/cm. Use Table 6 to interpretcalled ions. The important ions in water the figure. The units used in Western 55
  • 65. IONS The world is composed of chemical elements. We normally see only a few of these elements by themselves. These few include carbon (diamonds, graphite), sulphur (dusting sulphur), iron, zinc and aluminium. More often we see elements in combinations that are called compounds. The first two columns of Table 5 list a few of the many compounds that are soluble in water. When these compounds are dissolved in water, their two ‘halves’ split apart to form two parts that are called ions. One part takes on a positive electrical charge. Diamonds – one form of carbon. These are called cations (pronounced ‘cat-eye- ons’). The other part takes on a negative charge. The physical properties of soils are greatly These are called anions (‘an-eye-ons’). Table 5 lists influenced by the types and proportions of the the ions formed by the compounds listed. cations of calcium, magnesium and sodium that are present on particle surfaces. Ions are very important because: Whether a soil is acid or alkaline is determined It is mainly as ions that plant nutrients are held by the concentration of hydrogen ions in it. in soils. When plants are damaged by salty water, the It is mainly as ions that nutrients are taken up extent of damage depends on the concentra- by plants. tions and types of ions that are present. Table 5. The ions of some common water-soluble compounds Common name Chemical name Chemical formula Cation Anion + Baking soda Sodium bicarbonate NaHCO3 Na HCO3– 2+ Epsom salts Magnesium sulphate MgSO4 Mg SO42– + Sulphate of ammonia Ammonium sulphate (NH4)2SO4 NH4 SO42– + Potassium nitrate Potassium nitrate KNO3 K NO3– + Common salt Sodium chloride NaCl Na Cl– Pool acid Hydrochloric acid HCl H+ Cl–Australia are milliSiemens per metre (mS/m). An EC number tells you how salty your water1 dS/m = 100 mS/m. 1 mS/m = 10 µS/cm. is but it does not tell you anything about theThose not on a municipal supply should have concentrations of the different ions present.the EC of their water determined by a Some ions are much more damaging to plantslaboratory. A hydroponics shop might even do and soils than are others. The ions that causeit for nothing. the most damage are sodium, chloride,56 GOOD GARDENS WITH LESS WATER
  • 66. Table 6. How to interpret EC readings EC range (µS/cm)* Interpretation 0–500 Very low to low salinity, suitable for all plants. Municipal water supplies in Tasmania, southern Victoria, coastal NSW, SE Queensland, far north Queensland and the Top End are all in this category. 500–750 Sensitive plants, including ferns and fuchsias, and the seedlings of plants from high-rainfall areas, show burn around the edges of leaves and leaf drop if they are repeatedly misted with water of this quality. Application to the soil or potting mix should cause few problems other than tip damage to plants with long narrow leaves. Some greywaters from laundries that use powder detergents have salinities in this range. 750–3000 Increasing numbers of species show reduced growth, burning of leaves and even death as EC rises through this range. Some greywaters from laundries that use powder detergents have salinities towards the upper end of this range. >3000 Unsuitable for irrigation except for highly tolerant plants being grown in sandy soils with excellent drainage. The water in swimming pools can have salinities in the range 3000 to 9000 µS/cm, with those in pools having salt-chlorinators being the highest. Sodium levels are very high. These waters must never be run onto gardens. * Western Australian readers need to multiply an EC number produced in their state by 10 to compare it with the numbers in this table.boron and bicarbonate. If your water has an How salts damage plantsEC above 500 µS/cm, you should find out Relative to low-salinity water, salty water slowsmore about it. Ask your water supplier or have seed germination, stunts growth and retardsyour water tested for sodium, calcium, flowering. Salty water damages plants inmagnesium, SAR (see Table 7), chloride, several ways.boron and total alkalinity. Use Table 7 tointerpret the information. Damage to plants by increased soil salinity Repeated addition of salty water to a soil gradually increases the concentration of saltsModestly priced salinity meters are available from Some swimming pool test kits are able to measure thehydroponics shops. total alkalinity of water. 6 – WATER QUALITY 57
  • 67. Table 7. How to interpret analytical results for water supplies Ion Interpretation Sodium <70 mg/L No problems. If >70 mg/L, increasing damage when applied to the leaves of sensitive plants. >210 mg/L Not suitable for watering sensitive plants. Many laundry powder detergents produce greywaters that have sodium concentrations in the range 200–700 mg/L. Chloride <100 mg/L No problems. If >100 mg/L, increasing damage when applied to the leaves of sensitive plants. >355 mg/L Not suitable for watering sensitive plants. SAR* <6 No problems. >9 Increasing problems for cracking clay soils. >16 Increasing problems for non-cracking clay soils. Boron <0.5 mg/L No problems for most plants. 0.5–3 mg/L Increasing numbers of plants show toxicity symptoms. Greywaters from laundries that use detergents that contain boron may fit here. >3 Unsuitable for watering. Total alkalinity# <100 mg/L Generally no problems. The municipal water supplies of all major coastal Australian population centres have total alkalinity concentrations below 100 mg/L. 100–150 mg/L May raise the pH of soils and potting mixes, but use of acidifying fertilisers can counter this. Greywater (wash plus rinse) from laundries that use liquid detergents have total alkalinities in the range 20–150 mg/L (on top of the alkalinity of the water itself). >150 mg/L Will raise the pH of soils and potting mixes. Grow only lime-tolerant plants. Alternatively, acidify the water with sulphuric acid; you will need professional help. Many bore waters and inland surface waters have total alkalinities above 150 mg/L. Greywater from laundries (wash plus rinse) that use powder detergents have total alkalinities in the range 40–1150 mg/L (on top of the alkalinity of the water itself). *SAR = sodium adsorption ratio. It takes into account the concentration of sodium in relation to calcium and magnesium. See the section on damage to soils, below. If your water has a high SAR you should seek professional help for using it successfully. # Expressed as mg/L calcium carbonate equivalent.in the water in the soil. These salts reduce the Damage to soil by sodiumamount of water that plants can get from a The sodium of salty water damages thesoil, and also cause the plants to divert energy structure of clay soils. What happens is thatfrom growth to water uptake. If you have to sodium gradually displaces calcium andapply salty water to your plants, you need to magnesium from the surfaces of particles inapply enough so that salts are leached down the soil, so creating a ‘sodic’ (high-sodium)through the soil below the plant’s roots. soil. As long as the irrigation water remains saline, the aggregates in the soil can remainThe book Grow What Where (see Appendix 1) intact, but if salinity falls (as during rain) thecontains an extensive listing of Australian aggregates fall apart. Particles ‘float off’ ornative plants of known high tolerance to disperse into the soil water. They can thensalinity. form a crust on the soil surface. This will58 GOOD GARDENS WITH LESS WATER
  • 68. drastically reduce the rate of infiltration ofwater into the soil.As rainwater penetrates further into a sodicsoil, it continues to cause aggregates to fallapart within the soil. Roots are less able topush their way through the soil. They aretherefore less able to reach water and plantnutrients. The damage caused by sodium islessened as the concentrations of calciumand magnesium in the water increase,because then the sodium is less likely toremain on soil particle surfaces. Put anotherway, ‘hard’ salty waters (those that reduce The tips and margins of these pansy leaves are beinglathering of soap, and have a low SAR) are killed by boron toxicity.less damaging than ‘soft’ salty waters, such asthose that have passed through water as a browning and burning of leaf edges andsofteners. Greywaters from laundries can tips and death of whole leaves. Leaf area ishave extremely high concentrations of reduced; there is less green plant to capturesodium (see Table 7). sunlight so plant growth slows. Because chloride and sodium are taken up fasterDirect damage to plants through leaves than through roots, salty waterThe chloride and sodium ions of salty waters containing them damages plants most rapidlyaccumulate at the outer edges and tips of the when it repeatedly bathes their leaves, asoldest leaves, where they kill cells. We see this during overhead sprinkling. The nutrient element boron is present in high enough concentrations in a few water supplies (mostly from bores) to damage sensitive plants. Violas, pansies and kiwifruit vines are especially sensitive: they are damaged by water with as little as 0.5 mg per litre of boron (see below for comment about greywaters). Damage by alkalinity High concentrations of bicarbonate in irrigation water will steadily raise soil pH, eventually to a level that will interfere withThe lower leaves of this tree were killed throughrepeated sprinkling with water of about 1000 µS/cm the supply of trace elements to plants thatsalinity. need acid soil. If the total alkalinity of your 6 – WATER QUALITY 59
  • 69. water is above about 150 mg/L, you should and therefore the total amount of saltgrow only those plants that tolerate alkaline added to the soil.soils (see Grow What Where for a list of Counter soil damage by sodium byAustralian native plants that would be applying gypsum, if testing shows that itsuitable). Plants from alkaline soils elsewhere will be beneficial.in the world (the soils of many desert areas Do not let the soil dry out, as this willare alkaline) could also be grown. cause the concentration of salts in the remaining water to become very high. ThisWaters with total alkalinities above about effect is greatest in sandy soils.100 mg/L will steadily raise the pH of potting Leach excess salts from the soil. Leachingmixes. You can counter total alkalinities of up is easiest when soil structure is good. Ifto perhaps 150 mg/L through the use of possible, each time you apply saline wateracidifying fertilisers (those whose nitrogen is add 10–20% more water than is needed tosupplied mainly by ammonium and urea), but fill the soil reservoir (Table 3).water with higher total alkalinity is unsuitable When using salty water on potted plants,for use on potted plants. you should add enough water each time toGreywaters from laundries can have allow 5–10% to drain from the pots.extremely high total alkalinities (see Table 7). Do not water plants with salty water thatIf you do not want your soil to become has passed through a water softener. Thesealkaline, use liquid laundry detergents (see remove calcium and magnesium from thewww.lanfaxlabs.com.au/laundry.htm). If you water and replace them with sodium.have to use water with a total alkalinity above100 mg/L, every three to six months youshould check the pH of the soil to which it Using greywaterhas been applied. Apply sulphur if the pH is The term ‘greywater’ is used to describe thetoo high. Applications to reduce pH by one waters that flow from our showers,unit range from about 25 g/m2 for sands to washbasins and laundries. All stateabout 100 g/m2 for clay soils. governments now allow greywater to be usedNote also that some herbicides are inactivated on gardens, subject to various conditions.when solutions of them are made up with Water restrictions have forced manyalkaline water. gardeners to recycle greywater to their gardens. For this activity to be free from problems, there are a few essentials that mustMinimising damage by salty water be observed. Keep the water off leaves. Misting with Greywater from the shower, bath and salty water is particularly damaging. Use bathroom basin contains small amounts of drippers. soap, shampoo, conditioner, skin cells, urine Reduce evaporation from the soil through and perspiration. The concentrations of these mulching. This will reduce total water use are low and they are mostly readily degraded60 GOOD GARDENS WITH LESS WATER
  • 70. by soil microbes. This type of greywater can Sodium concentrations in effluent ranged frombe used on any plants that tolerate the salinity about 710 mg/L to about 35 mg/L.of the incoming water used to create it.Because bathroom greywater quickly becomes The concentrations in effluents producedsmelly, it should be applied to the garden from liquid laundry detergents ranged fromwithin a few hours of its production. about 130 mg/L to less than 2 mg/L.Bathroom greywater that contains hair dyes, You already know that sodium added to a soilbleach and disinfectants should not be used displaces calcium and magnesium from clayin the garden. particles. With addition of enough sodium,Greywater from the laundry has the potential the soil will become sodic. So if youto cause serious problems. Many laundry repeatedly apply greywater containing highdetergent powders consist largely of various concentrations of sodium to your soil, you willfillers, mainly sodium salts such as sodium inevitably cause the soil to become sodic. Thesulphate and sodium bicarbonate, with only high concentration of salts in the greywaterabout 15–20% detergent. Laundry greywater will at first mask the adverse effects of thiscan contain very high concentrations of sodicity, so lulling you into a false sense ofsodium and phosphorus and can be very security. But as soon as the salts are dilutedalkaline. If you do want to use greywater from with the next rain, all the bad effects ofyour laundry in your garden, you MUST take sodicity – slow water infiltration, damagednote of the following if you are to avoid soil structure, surface crusting – will show up.creating serious problems for your soil and The only way back from this mess is to apply aplants. But when you use a non-polluting source of calcium (gypsum or a solublelaundry detergent (see Table 8), you can use calcium product, see p. 36) and use rain orboth the wash and rinse water on your considerable amounts of extra irrigationgarden. If you use a detergent that gives water to leach the sodium out of the topsoil.slightly higher concentrations of sodium and It is far more sensible to prevent this damagealkalinity than do these non-polluting in the first place by using a laundry detergentdetergents, you could let the wash water run that has a low sodium content but still givesto the sewer and the rinse water to the you effective laundry performance. There aregarden. now many products to choose from.Sodium PhosphorusLaundry detergent powders all have much The phosphorus in laundry detergents ishigher concentrations of sodium than do the present as phosphates that help remove dirtliquid detergents. Lanfax Laboratories of from clothes. Choice magazine (see issues ofArmidale, New South Wales have published the June 2005, April 2007) has shown thatresults of analysis of effluent (wash plus rinse) laundry detergents that do not containproduced from over 100 laundry detergent phosphorus generally do not clean heavilypowders (see www.lanfaxlabs.com.au). soiled clothes as well as do those that contain 6 – WATER QUALITY 61
  • 71. Even native plants that are generally tolerant of phosphorus can be damaged by high additions of phosphorus.Shown here are leaves (left upper surface; right lower surface) from young trees of Corymbia maculata (SpottedGum), C. citriodora (Lemon Scented Gum), Eucalyptus leucoxylon rosea (SA Blue Gum), Angophora costata(Smooth-barked Apple) and Lophostemon confertus (Tristania). The purple spotting and pustules are the resultof severe phosphorus toxicity. The trees had been continually watered with high-phosphorus (14 mg/L)greywater. Powder laundry detergents with the highest phosphorus contents produce greywaters (wash plusrinse) with phosphorus concentrations in the range 20–80 mg/L!phosphorus. However, if you want to use additions of this greywater will soon start tolaundry greywater on your garden, you need produce problems. The 75 L of water fromto choose between having ‘very clean’ clothes one wash would typically be applied to about(and potentially damaged soil and polluted 25 m2 of garden (so giving an application ofgroundwater) and slightly less clean clothes 3 mm of water). Weekly application to the(and not polluting your environment with same area for a whole summer would deliverexcessive phosphorus). You will probably only over 5 g phosphorus/m2. This is several timessee the difference in white clothes. the annual amount of phosphorus removed in clippings from a domestic lawn and dozens ofThe concentrations of phosphorus in the times more than is needed by ornamentaleffluent waters reported at www.lanfaxlabs. trees and shrubs.com.au ranged from 80 mg/L to zero.Products that contained the lowest Application of these huge amounts ofconcentrations of sodium had no or very little phosphorus to a garden soil will soon startphosphorus (Table 8). For those products to cause problems, including greater attackwith the highest concentrations of by mildews and insects on the lush plants,phosphorus, the total amount in a typical and interference with the use of tracewash (wash plus rinse) was 6–8 grams. elements by plants. Drought-tolerant plantsIf you apply this high-phosphorus greywater will use much more water (see p. 24). Withto a soil that has an inadequate supply of repeated applications, your plants may notphosphorus for the plants being grown, you be able to extract enough trace elementswill see that your plants put on luxuriant from the soil. If this type of greywater isgrowth. But don’t be fooled. Repeated applied to plants that are sensitive to62 GOOD GARDENS WITH LESS WATER
  • 72. Table 8. Sodium, phosphorus and alkalinity in laundry greywaters (wash plus rinse for top-loading machines and 150 Lwash cycle volume) for some laundry detergents with low soil-damaging potential Alkalinity (mg/L calcium Laundry detergent# Sodium (mg/L) Phosphorus (mg/L) carbonate) Powders Aware Environmental Concentrate 90 0 190 Planet Ark 80 0 170 Biozet Advanced Concentrate 70 2.8^ 100 Amway SA8 25 0 40 Liquids Earth Choice Laundry Liquid 5 0 20 Savings 4 0 20 Home Brand 2 0 20 Eco-wash* 0.5 0 1 # Note that manufacturers may from time to time change formulations. ^ Packages in supermarkets in late 2007 carry the label ‘NP (no phosphorus)’. * Lanfax Laboratories data from the producer Sage Horticultural. Source: www.lanfaxlabs.com.auphosphorus (see p. 26), within weeks you How to divert and use greywaterwill see that they start to yellow and In all states, greywater can be diverteddie. This effect of excessive phosphorus direct to your garden without the needwill show up first, and be most severe, on for a permit, but you must apply itsandy soils. immediately or within 24 hours of producing it. The website www.health.nsw.If you do have to use a powder detergent that gov.au gives a good summary of typicalcontains phosphorus, choose one that has a regulations. If you want to store greywaterlow concentration and use the greywater for longer than 24 hours, you must install ancontaining it only on those plants whose approved treatment system.parts are to be harvested (fruit trees,vegetables, cut flowers, bedding plants).Applying only the rinse water to drought-tolerant plants growing in clay soils maybe acceptable, but this greywater mustnever be applied to phosphorus-sensitiveplants (p. 26).BoronDo not use a detergent that contains boron(listed as ‘perborate’ on the detergent Where the laundry drain is easily accessible, thispackage), because it can build up to levels in simple device allows the greywater to be eitheryour soil that are toxic to plants. diverted to a surge tank or to run to the sewer. 6 – WATER QUALITY 63
  • 73. One diversion method is to install 3-way diverters into the pipes from the laundry and bathroom and divert the water direct to the garden. A better method is to divert the water into a surge tank from which it can flow or be pumped into greywater dripper lines. In fact, because washing machine pumps are damaged if flow from their greywater outlet is restricted in any way, it is essential that you let the washing machine pump the water into a surge tank. Make sure that fittings in lines do not restrict flow. Do not try to pump directly into dripper lines. The surge tank can be a recycled 200 L drum (see the Yellow Pages for drum recyclers) or one of the many manufactured systems. A 20 watt submersible pump as used for aquariums and smallGreywater diversion at its simplest. On sloping sites,gravity, rather than a pump, may be enough todistribute the water. If the outlet is at the base, youcan completely drain the drum by slightly tilting it.If you are distributing greywater via a (lilac-coloured)dripper line, you must install a pond pre-filter such asthis to prevent fine lint from clogging drippers. Specially modified wheelie bins (shown in cutawayAlternatively, a long ‘sausage’ of fine cloth over the image) offer an economical way of catching andend of the greywater inlet into the drum will remove diverting laundry greywater. The small amount notlint, but it must not restrict flow from the washing removed by the pump is easily removed via a drainagemachine. plug. (Photo: Just Water Solutions)64 GOOD GARDENS WITH LESS WATER
  • 74. In addition: Pipes that carry greywater should be labelled to show that the water is not suitable for drinking. Do not apply greywater to soils within 1 m of boundary lines. Do not use greywater from the kitchen. Fats and oils in it can harm soils. However, you could collect and use non-fatty kitchen rinse water. Apply greywater via slotted pipe buried in gravel-lined trenches in the soil or via dripper lines that are installed under mulch. The water must be filtered before going into dripper lines. Pond pre-filters may only need monthly cleaning, but cloth filters willAnother type of greywater diversion system. The surge probably need more frequent cleaning.tank comes in 80 and 500 L capacities. (Photo: ESA Slotted pipe and dripper lines should beEnvirowater Pty Ltd) fitted with ends that can be opened to allow flushing. Have a regular maintenancehydroponics systems will pump water for short program.distances (up to perhaps 15 m through The plumbing for greywater distribution12 mm hose) from a low-level surge tank. should be easily accessible in case blockagesYou must observe the following precautions, need to be removed. Flush the whole systemespecially in built-up areas. every couple of months.The water must not: Any human pathogens in greywaters are rapidly killed by soil microbes, especially if smell bad there is plenty of organic matter in your soil. form ponds on the soil surface run onto neighbouring properties, into Problems from greywater use will be least if swimming pools and water features or into you match the application rate to the streams infiltration rate of your soil. In particular, a pollute the groundwater low rate of application to a large area is be applied to soils above an aquifer that is preferable to a high rate to a small area. As a used as a source of drinking water rough guide, if your laundry produces 400 L be applied to the garden via sprinklers of greywater each week, in summer this needs be applied around leafy vegetables that are to be applied to at least 15 m2 in hot areas to be eaten raw. and to at least 30 m2 in cooler areas. These 6 – WATER QUALITY 65
  • 75. Compare systems on the basis of level of treatment you need, cost, size of tanks in relation to space available, service costs, maintenance needed, power consumption, number of moving parts that can break down, noise, use of toxic chemicals, odours produced and provision of warning of malfunction. Water quality and potted plants All the earlier comments about water qualityExample of the greywater treatment systems that mustbe used if you want to store greywater for later use. apply to plants in pots, but there are a few(Photo: Nubian Water Systems) extra details that need to be considered. If your main method of watering is fromapplication rates are 26 and 14 mm/week, below, for example by wick or from a capillaryrespectively. Application rates must be lower mat, occasionally water from above to leachat cooler times of the year, down to nil when out excess salts. How often ‘occasionally’ isthe soil is already at field capacity. depends on the salinity of the water used and on the evaporation rate, but it could be onceOver-application of greywater can be a month for very salty water. When the waterprevented through the use of the FullStopTM is pure, and fertiliser use not excessive,wetting front detector (see p. 80). leaching might only be needed every coupleIf you want to store greywater for longer than of years.24 hours, you must install an approved When your water is salty, don’t let the mixtreatment system. These systems use filters, become too dry between waterings. Apartbiological systems, chemicals or UV light to from the obvious effects of drought on plants,kill microbes in the water. Inevitably, these the water remaining in a dry mix can besystems are expensive, but rebates are lethal to plants because of its very high saltavailable from some state governments. concentration.There are now about a dozen systems tochoose from. They must be installed by a In hot weather the combination of too muchspecially licensed plumber (see www. controlled-release fertiliser and a rapidlygreenplumbers.com.au). You must get drying mix can quickly give plants a lethalapproval from state and council authorities. dose of salinity.66 GOOD GARDENS WITH LESS WATER
  • 76. D ELI V ER I N G WAT ER TO YOUR PL A N TS KEY POINTS Make the most of rain Five simple steps to delivering the right amount of water to your plants Useful devices – controllers and sensors How to water-proof a medium-sized gardenNot so long ago in most of Australia, experience in your garden. You know that youit was possible to apply to gardens as much are likely to live longer and suffer fewerwater as was needed to keep them lush. illnesses if you garden than if you do not. ButSprinkler systems hooked to electronic with restrictions on the use of water, how cancontrollers could be programmed to you continue to garden? The good news isdeliver water when needed, without that you can, but you probably will need torestriction. Much of the drudgery of make some changes to your garden and thewatering during months of rainless heat way you manage it.had been removed. This chapter is about getting the most out ofThe combination of drought and rising both the rain that you do receive and thepopulation has radically changed all this. water from the municipal supply that you areWhile watering by drippers is still allowed in allowed to use on the garden.many parts of the country, there areincreasingly large areas where buckets filledwith greywater are all that stand betweendrought-sensitive plants and death. Make the most of rain You must make sure that:You are reading this book because you want agarden. You like to tend plants; you like the as much as possible of the rain that fallsway plants keep your house cooler on hot onto your soil actually soaks into it (see thedays; you like the relaxation that you section on infiltration on p. 47). 67
  • 77. water that falls onto paths and driveways flows onto the garden. Pavers allow some of the water to penetrate between them into the soil below, where the roots of trees and shrubs can use it. as much as possible of the rain that falls on the roof of your house and sheds is diverted either directly to the garden or via storage tanks.You should also seriously consider storing The Rainstore3 system uses a modular framework maderainwater under your driveway and other non- from recycled plastic to support the pavement, so onlygarden outdoor areas such as patios. Two of a small proportion of the total storage space is taken upmany available systems are illustrated. A small with support material. (Photo: Invisible Structures)solar-powered pump can be used to apply thestored water to the garden. Benefits of rain Gardeners often notice that after rain, their plants look much lusher and healthier than when the only water they get is via irrigation. Why does this happen? Several factors seem to contribute: Rain washes dust from leaves, so the green is not masked. Rain always gives more uniform watering than even the best irrigation system, so all plants get a drink. The air during and soon after rain has a higher humidity than at other times. Plant leaves remain turgid and more erect. Salt build-up in the soil will be diluted or removed, so enhancing plant uptake of water. Rain, particularly from thunderstorms, brings with it some extra nitrogen. This could ‘green up’ plants that are a little deficient in nitrogen.The University of South Australia porous paver systemhas a confined gravel bed for storing water that Another effect of rain is that it washes somepercolates through the large gaps between the pavers.With this system, it is possible to collect and store plant nutrients, especially potassium, from8000 L of water under a double driveway. leaves. If the water then falls on soil below the68 GOOD GARDENS WITH LESS WATER
  • 78. Potassium deficiency in Dracaena fragrans. (Photo:Keith Bodman)plants, the nutrients are quickly recycled backinto them. But if the water instead falls on a Small water features give tranquillity to a garden. Theyhard surface and is carried away, the plants in can be filled by diverting rainwater from a small roof.this area can eventually run short of one ormore nutrients. Potassium deficiency nurseries and racecourses. No doubt more ofsymptoms are common on trees in hard- this stormwater will be collected and used inpaved areas. the future, but it makes sense if more of it is used where it falls. Here is how you can get the most out of ‘your’Diverting water from the roof rain:The rain that falls on the roofs of houses in Install the largest rainwater tank or tanksurban Australia is mostly diverted via gutters that you can fit in. For an average houseand spouting to the gutter beside the road 5000 L is a minimum, with at leastpavement at the front of the house (the so- 20 000 L desirable for larger blocks. Thecalled street water table). A small amount is water you collect will cost you more thancollected in rainwater tanks, with the does the water from your supply authority,overflow going to the street. With increasingly but it is still a bargain if that authority hasdense urban housing, the volume of water banned or severely restricted the use of itsfrom a modest rainfall event can be enough water on your garden. Your stateto overload the whole stormwater system and government or local council probablycause flooding of lowland areas. offers a subsidy for new tank installations.In this driest inhabited continent, this is the (Relative costs – municipal water: aboutheight of lunacy. A bit of this stormwater is $1.25 per kilolitre (kL); tank water: aboutcaught in wetlands from where it can be $4 per kL if the tank lasts 20 years and youpumped underground for later use in parks, collect and use about twice the capacity of 7 – DELIVERING WATER TO YOUR PLANTS 69
  • 79. Even the smallest city garden can have a rainwatertank. Note the first flush diverter on the left. the tank in a year; ‘spring’ water purchased in 600 mL one-use plastic bottles: about $4300 per kL at convenience stores; imported bottled water in upmarket restaurants: $8900 to $17 000 per kL.) For water of the highest quality and for minimal hassles with blockages, install gutter guards, gutter screens and a first-flush diverter between roof and tank. The first-flush diverter can also double as a means of preventing contamination of the tank when you clean the gutters. Screens must be regularly inspected and cleaned. Reduce leaf drop into gutters by removing tree branches that overhang the roof. Mosquitoes can be stopped from breeding in the tank by having screens over inlets and outlets and/or by regularly (after each overflow and weekly during summer) applying domestic kerosene to the water at 1 teaspoon per tank. Do not use power kerosene as it will taint the water. Have the tank base as high as is possible. Of course the roof water must still run into Essential parts of a rainwater collection system (from the tank, but the higher the base the top): gutter guards, leaf screen, first flush diverter.70 GOOD GARDENS WITH LESS WATER
  • 80. greater the pressure you will have forgravity feeding the water to your garden orto taps inside the house.Install the tap on the tank in such a waythat it is easy to connect it to a drippersystem that will water your most valuableplants. You may need to install a pump sothat there is enough pressure for thedrippers to function effectively. For atypical dripper line, you need only This small pressure pump is all that is needed to pumpinstall a small pressure pump that is water from a tank to a dripper or micro-sprinklercapable of supplying about 10 litres of system.water per minute.Arrange the overflow outlet of the tank so In areas of low average annual rainfallthat overflow water can flow either to the (certainly wherever the long-term averagestreet or be applied to your garden. A annual rainfall has been up to 500 mm; itmain reason why governments have is now rather less than this), it is alsorequired stormwater to be diverted to the desirable to divert to the garden all or moststreet is concern that the water may of the rain that falls in the wetter part ofotherwise cause problems by flooding the year. By allowing this to soak into yourneighbouring properties. You can soil, you can fill up the subsoil with water.therefore only divert overflow water to the The deep-rooted, drought-tolerant plantsgarden when you are sure that it will all that you will be growing will then have asoak into your soil and not run next door. better supply for the dry times.Overflow water from rain that falls during For a small garden around a house of averagethe dry season will be a particularly size, it is entirely possible to provide all thevaluable addition to your garden. Every water for the garden from rain plus greywatereffort should be made to use every drop (see detail at the end of this chapter).of it.One way of coping with a heavy flow ofwater during the dry season is to connect alength of flat hose to the tank outlet. Theother end can be shifted around thegarden during the rain. A good option forsloping sites is to run the water through alength of 50 mm slotted plastic drainagepipe laid out across the top of a slope. Thewater will trickle out through the manyholes in the drainage pipe and so bespread across the garden. No cheating here! 7 – DELIVERING WATER TO YOUR PLANTS 71
  • 81. Ornamental plants of medium drought tolerance (see Table 10): less than once a week in summer grading to none in winter. Drought-tolerant ornamental plants: never in many areas, grading to twice a summer and certainly no more frequently than once a month in the driest part of the year, unless they are planted densely. Each watering is to be of at least 60 mm. Five simple steps to work out how muchThe plants in these planter boxes are watered via water to apply to different parts of yourbuilt-in reservoirs that greatly reduce wateringfrequency. (Photo: a2zplanters) garden To work out the amount of water to be applied to each area of your garden, you needThe frequency of water application is answers to the following questions:different for different types of plantsThe basic philosophy is that water is applied 1. What is the drought tolerance of theas infrequently as the plants being grown can plants in the area?tolerate, to hold off watering during and for 2. What was the average amount of watersome time after rain, and to decrease evaporation in your locality during thefrequency as temperature falls. The range is previous week?as follows: 3. What is the minimum quality level that you will tolerate for the plants in this Vegetables that are producing abundantly, area? and potted plants: daily in hot/dry 4. How much water does the irrigation periods to less frequently in cooler/wetter system of this area deliver each hour? weather. 5. What were the actual weather conditions New plantings: twice a week for two weeks during the previous week? if establishing them during cool weather, then gradually decrease frequency to that Detailed guidelines for finding answers to of established plants; daily for two weeks if these questions are given below. Even if you establishing them in warmer weather. are going to have a soil moisture sensor or an Including a water crystal slurry in the on-site weather station manage your planting hole can reduce the need for irrigation system for you, it is still necessary extra water (see p. 110). that you have answers to questions 1, 3 and 4. Fruit trees: weekly during summer, but Evaporation and local weather conditions are perhaps twice a week in the middle of a automatically covered by sensors and weather prolonged heat wave. stations, but you must be able to set the72 GOOD GARDENS WITH LESS WATER
  • 82. controller for each of the different areas of plants and exotics may never need to beyour garden according to plant needs and watered after establishment, whereas awater delivery rates for each area. mixture of drought-tolerant and drought- sensitive plants would need repeated watering. This latter arrangement would useStep 1. Drought tolerance of plants much more water than would separateGeneral information about drought tolerance plantings. What is more, the drought-tolerantis given in Chapter 2, and specific plants could well have shortened lives throughinformation for lawn grasses is given in excessively rapid growth or the developmentChapter 12. Use this information in of root rots.conjunction with the ‘crop factors’ in Table 10to work out a watering schedule for different If you know in advance that you will not beparts of your garden. able to provide extra water to some of your plants, you could improve their chances ofIf you want vegetables, fruit trees, herbs and surviving summer by reducing their canopyannual bedding plants to produce size. Remove branches or just cut back foliageabundantly, you will have to treat them as if all around, whichever looks best.they cannot tolerate drought.Of all the plants that you will want to grow in Step 2. Evaporation of water in your areacontainers, only the succulents and cacti will Table 9 lists average evaporation rates forsurvive if they are not watered frequently in major Australian population centres, plus asummer. few others for contrast. These figures are theIt is absolutely essential that you group plants depths of water that will evaporate from aof similar water requirements. For example, a ‘Class A pan evaporimeter’ in one week undercorner of drought-tolerant Australian native average conditions for the location. Losses from plants will always be less than this, as you will see in the next section.Increasingly, plants in nurseries are being labelledaccording to drought tolerance. Evaporimeter operated by the Bureau of Meteorology. 7 – DELIVERING WATER TO YOUR PLANTS 73
  • 83. Table 9. Approximate weekly depths of water evaporated from an evaporimeter in various parts of Australia (mm per week) Place Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Annual Coastal mm Hobart 30 27 20 13 9 6 6 8 14 19 24 27 1000 Melbourne 41 39 28 18 11 8 9 13 18 25 32 38 1500 Brisbane 39 35 31 26 18 16 16 22 29 34 38 44 1700 Adelaide 50 47 34 21 13 10 10 15 21 30 40 45 1900 Sydney 50 45 37 29 20 18 19 26 34 41 45 52 2000 Perth 57 54 43 28 19 14 14 17 24 35 39 44 2000 Townsville 58 51 49 46 38 35 37 43 54 62 64 63 2800 Darwin 45 41 43 48 50 49 50 53 56 58 55 49 2400 Inland Canberra 49 42 31 19 11 8 8 13 20 28 38 48 1800 Mildura 74 69 52 32 18 13 14 20 31 45 60 71 2100 Alice Springs 90 80 70 51 34 25 27 39 55 71 80 85 3000 Oodnadatta 115 105 85 58 38 28 32 43 60 81 99 113 3100 Source: Bureau of Meteorology; www.bom.gov.auStep 3. Minimum plant quality tolerated from an evaporimeter as 1, a use rate of 85%You need to decide what quality you would of this will be given as 0.85 and 20% as 0.2.like your plants to have. At one end of the These numbers are called crop factors.scale, the plants will look lush and be growing Table 10 lists crop factors that are associatedvigorously. At the other end of the scale, they with different levels of plant growth andwill be just hanging in. Of course, if the appearance.plants have a high tolerance to drought, they How to use evaporation figures and cropcan still look excellent, even though ‘ just factorshanging in’. Using evaporation figures and crop factors isResearch has shown that, when all types of easy.plants are provided with unlimited water,they will use water at about 85% of the rate at 1. From Table 10, choose a crop factor thatwhich it is lost from a nearby pan matches the type of plant growth you want.evaporimeter. But when plants have access to 2. From Table 9, choose evaporation figuresless water than this, they use water at a lower for your area.rate. This decreases their growth rate, but it 3. Multiply the appropriate evaporationdoes allow them to ‘stretch out’ the supply in figure by the crop factor to get the amountthe soil. Highly drought-tolerant plants can of water needed by your plants each week.in fact survive while using less than 20% of Example 1: vigorous lawns, Melbournethe water that is being lost from a nearby panevaporimeter. We can express these numbers You have one cool-season grass lawn and onein another way. If we give the rate of loss warm-season grass lawn. If you decide that74 GOOD GARDENS WITH LESS WATER
  • 84. Table 10. Crop factors for different types of plants that are You do not have enough water allocation tobeing maintained to different levels of growth allow the cool-season grass lawn to continue. Type of growth or Crop You decide to convert it to plantings of Plants appearance factor Vegetables, Ample produce 0.85 drought-tolerant plants, including some fruit trees Australian native plants and some succulents. Lawns, cool- Lush 0.8 The crop factor for them is 0.2. You are season grass Strong growth 0.7 prepared to accept a somewhat lower quality Moderate growth, just 0.65 for the warm-season grass lawn, so the crop acceptable factor for it will be 0.3. The calculations will Lawns, warm- Lush 0.6 season grass give the results shown in Table 12. Strong growth 0.5 Some growth, just 0.3 Now compare these figures with rainfall acceptable quality figures for Melbourne (Table 13). Ornamentals Establishment, vigorous 0.8 growth, large-leaved You can see that established drought- Strong growth 0.65 tolerant plants should be able to survive Moderate growth, 0.4 somewhat drought-tolerant without any extra water other than that plants provided by rain. For this to be possible, Low growth rate 0.2–0.4 acceptable, plants drought- it is necessary that winter rain soaks into tolerant the soil for use during the drier months. Minimum; desert plants 0.1–0.15 (If you do not get much winter rain, your plants will struggle, but if truly drought-you would like them to put on strong, but not tolerant should survive.) The warm-seasonlush, growth, the crop factor for the cool- grass lawn may need no more than one deepseason grass is 0.7, and for the warm-season soaking in January.grass it is 0.5.You can see (Table 11) that a lawn of warm- Step 4. Amount of water delivered by yourseason grass will need much less water than a irrigation systemlawn of cool-season grass. The simplest way of finding out how muchExample 2: drought-tolerant plants, water is delivered by a section of yourMelbourne irrigation system is as follows:Table 11. Results of calculations to determine weekly amounts of water to apply to lawns composed of cool-season orwarm-season grasses that are growing strongly Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Evaporation (mm/week) 41 39 28 18 11 8 9 13 18 25 32 38 Type of plants Amounts of water needed each week (mm) to maintain the chosen level of growth Cool-season grass 29 27 20 13 8 6 6 9 13 18 22 27 (crop factor 0.7) Warm-season grass 20 20 14 9 5 4 5 6 9 12 16 19 (crop factor 0.5) 7 – DELIVERING WATER TO YOUR PLANTS 75
  • 85. Table 12. Results of calculations to determine weekly amounts of water to apply to a lawn composed of warm-seasongrasses of just acceptable quality and an area of drought-tolerant plants Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Evaporation (mm/week) 41 39 28 18 11 8 9 13 18 25 32 38 Type of plants Amounts of water needed each week (mm) to maintain the chosen level of growth Drought-tolerant plants 8 8 6 4 2 2 2 3 4 5 6 8 (crop factor 0.2) Warm-season grass 12 12 8 5 3 2 3 4 5 8 10 11 (crop factor 0.3) Read the water meter. Water meters used Measure the area of the garden watered by in Australia read to 0.1 or 1 litre. this section of your irrigation system, in Run the section of the irrigation system square metres. Pacing it out will do. you are checking for exactly 10 minutes. Divide the number of litres delivered per Do not use any water elsewhere during the hour by the number of square metres test period. watered to get the number of litres Read the water meter again. delivered per square metre. This is the The difference between the two readings number of millimetres depth of water gives you the number of litres of water that delivered. were delivered to this section of your Example garden in 10 minutes. Multiply the number of litres by six to get The number of litres delivered in 10 minutes the number of litres delivered in one hour. was 50.Table 13. Median weekly rain (mm) Place Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Coastal Hobart 8 7 7 8 8 7 8 11 9 10 9 11 Melbourne 10 6 8 10 10 9 9 11 10 13 13 10 Brisbane 32 29 28 15 13 11 9 7 10 13 13 10 Adelaide 6 2 5 8 14 21 17 18 15 11 8 6 Sydney 18 20 21 20 20 23 13 11 12 12 17 13 Perth 0.5 1.5 2 9 14 41 39 30 16 10 5 2 Townsville 50 56 35 8 5 2 1 1 0.5 3 8 19 Darwin 102 88 73 19 1 0 0 0 1.5 13 35 54 Inland Canberra 12 13 8 8 10 8 9 11 13 14 14 10 Mildura 3 2.5 1.5 3 4 4 6 6 6 6 4 3 Alice Springs 3 4 3 0.5 2 1 1 0.5 0.5 5 5 6 Oodnadatta 2 3 0.5 0.5 1 1 0.5 0.5 1 1.5 1.5 3 Source: Bureau of Meteorology; www.bom.gov.au76 GOOD GARDENS WITH LESS WATER
  • 86. ANOTHER USE FOR THE WATER M E TER From time to time you should look at the water meter when all devices that use water are turned off. If the meter is showing water use, you probably have a leak in the plumbing that must be found and fixed. It is January.This water meter reads 73 489.1 litres. The average evaporation figure for a week is 41 mm.Therefore the number of litres that would bedelivered in 1 hour is 6 50 = 300 L. An area of shrubs of moderate drought tolerance is to be watered. The crop factor isThe area watered was 30 square metres. 0.4, so you would apply 41 0.4 = aboutTherefore the number of mm depth of water 16 mm of water.delivered was 300 ÷ 30 = 10 mm per hour The dripper system to this area delivers water(One litre spread over one square metre gives at the rate of 10 mm per hour.a water depth of exactly 1 mm). You therefore need to run the drippers for 16 ÷ 10 = 1.6 hours.Step 5. Putting it all togetherLet us continue the example for Melbourne Variationsstarted above. 1. There were a couple of light showers during the week. None of this water penetrated to the soil through your mulch, so all the plants got was what fell onto their leaves. Transpiration would have been reduced during and after the showers. Reduce dripper running time by about 10%, to 1.4 hours. 2. There was a heavy shower during the week that delivered 8 mm. You canA very useful alternative for measuring the output of reduce the application from 16 mm tosprinkler systems is to use tin cans. You measure with 8 mm. So you run the drippers fora ruler the depth of water (in mm) caught in each can 8 ÷ 10 = 0.8 hour.and then calculate an average. This method also givesyou information about the uniformity of application 3. The maximum temperature on threefrom the sprinklers. days during the week was in the 38–42°C 7 – DELIVERING WATER TO YOUR PLANTS 77
  • 87. range. The evaporation rate during these days would have been double the average. Evaporation could have been 45% higher than average for the week, i.e. 41 1.45 = 59 mm. So apply 59 0.4 = 24 mm of water. You need to run the drippers for All your calculations will be useless if roots from next 24 ÷ 10 = 2.4 hours. door suck large amounts of water from your garden.4. Water use by moderately to highly RootBarrier® is an effective, non-polluting way of drought-tolerant plants is least when they preventing such ‘theft’. (See www.rootology.com.au) are allowed to become somewhat stressed between applications. Extend the times A suggested strategy between waterings into the four-to-eight When you got to the ‘Variations’ section week range. Each application would be above, you probably started to think that this about two-thirds the sum of the is all too hard. You realise that all the calculated weekly amounts. numbers are averages, and no week is average.It is late March. Besides, evaporation figures for capital cities are measured in open areas near city centresThe average weekly evaporation figure is or at airports. Your area may be higher and28 mm. cooler, with lower evaporation, or it could beContinue with the example of drought- windier, with higher evaporation. Even withintolerant shrubs used above. Crop factor 0.4, so your garden, water loss rates will be higher onweekly application needed is 28 0.4 = 11 mm. the north and west sides of the house than on the south and east.You could run the drippers for a bit over onehour, but a preferred alternative (on the Before you throw up your hands and decideprinciple of deep, infrequent watering) would to go back to guessing, try the followingbe to wait another week and then run the simple strategy.drippers for two hours. Start with simple calculations like thoseExample for vegetables in Adelaide in January above, based on the information provided here for your area.Weekly evaporation is 50 mm. For a few weeks, apply the calculatedCrop factor for vegetables 0.85. amounts of water.Weekly water needed 50 0.85 = 42.5 mm. If all the plants are happy, recalculate watering amounts using lower crop factors.Tank water is to be applied daily so that the That is, put on less water each time or,vegetables are not set back. Daily application preferably, extend the time betweenis 42.5/7 = 6 mm. waterings.If the drippers deliver 12 mm/hour, they If they are still happy after a few weeks, tryneed to run for 30 minutes each day. again decreasing the amount of water78 GOOD GARDENS WITH LESS WATER
  • 88. hardware store lines generally have limited capabilities compared with those that can be purchased at specialist irrigation shops. If you are still able to use an automatic system, choose one with as many as possible of the capabilities listed in the box on p. 81. Rain switches are small devices that can be added to controllers. They stop the controller from operating during rain and for a day or two afterwards (see www.smartwatermark.org for a list of approved sensors). Most do notTap timers at their simplest (left, all it can do is turn off take account of the amount of rain that hasthe system) … or (right) with the ability to be managed fallen. The delay until next watering stillautomatically with a soil moisture sensor.(Photo: Toro Australia) needs to be worked out manually. Soil moisture sensors provide a much more applied or, better, for drought-tolerant effective way of taking account of rain. plants, extend the time between waterings. Soil moisture sensors are buried in the soil in But if your plants are showing stress, and a watering zone of your garden that is set to you have the water allocation, increase the receive weekly applications of water during water amounts again. hot weather. This will usually be under a fruit If you do not have enough water, you need tree. The sensor cancels scheduled irrigations to replace drought-stricken plants with others that are drought-tolerant.All this becomes child’s play if you are able tolet a soil moisture sensor manage yourwatering for you, as outlined below.Useful devicesYour simplest aid is a tap timer. These rangein complexity from simple mechanical devicesto quite sophisticated programmable The Australian-made Watermatic soil moisture sensorelectronic devices that can even be managed is installed in the soil of an area that will be regularlywith a soil moisture sensor. watered. It has a proven track record from 20 years of use in sports turf applications, where it has consistently provided savings in water use of betweenTo automate the watering of multiple areas, 40 and 60% (compared with guessing or time-basedyou can choose from a wide range of application). (Photo: Cuming and Associates,programmable controllers. The cheapest Melbourne) 7 – DELIVERING WATER TO YOUR PLANTS 79
  • 89. The Australian-made AquaBlu™ soil moisture sensor isan urban-horticulture version of a sensor that has The FullStop™ wetting front detector is used underbeen successfully used in irrigated horticulture for fruit trees and vegetables, but not under moreover 10 years. (Photo: AquaSpy Group) drought-tolerant plants.when the soil is moist enough. The run times Not all soil moisture sensors are createdof the other zones are set to the needs of their equal. With some of the cheaper ones, theplants relative to the first zone, using the crop reading changes as the salinity of the soilfactors listed in Table 10. The whole system is changes. They give different results inthen self-controlling. Watering intervals are different soils. They may give satisfactoryautomatically decreased when the soil loses results if the salinity of your soil is fairlywater more rapidly in warm weather, and constant and you learn by trial and error howincrease as the weather cools or when rain to manage them.falls. During extended periods when the soilis moist, the sensor prevents the controller Keen growers of fruit and vegetables shouldfrom operating. These sensors will connect have a look at the FullStop™ wetting frontinto any controller, and will be easiest to detector (www.fullstop.com.au). (Themanage if the controller has the capabilities wetting front is the boundary between wetlisted in the box on p. 81. Once set up, they soil and the drier soil below it.) This simpleeliminate the need to do all the calculations device is only useful for plants growing ingiven earlier in this chapter. Trials in both the soil that is to be kept close to field capacityUSA and Australia (Melbourne and Perth) (see p. 50). It is not suitable for use underhave shown that correctly installed soil drought-tolerant ornamentals. It is verymoisture sensors are more effective than much an educational tool that will tell youweather-based methods for automatically what is happening in your soil when youmanaging watering. apply water to it.80 GOOD GARDENS WITH LESS WATER
  • 90. ‘ SM ART’ IRRIGATION CONTROLLER SThe smartest controller for managing watering from an on-site weather station. This method ofsystems is you, the gardener, armed with the operation is now widely used in the southern USAinformation just provided. You will know when to (see www.scwa.ca.gov and www.mwdoc.com forturn on the system and for how long to leave it on. examples). These controllers are available inHowever, there are some ‘smart’ controllers that Australia and can be managed with informationcan take out most of the hard work of managing a provided via an internet connection to www.bom.watering system. gov.au (the Bureau of Meteorology). This method of operation will be most reliable when the BoMThe best ‘smart’ controllers have the following weather station is within a few kilometres of yourminimum capabilities: garden. While this way of operating a controller allow non-watering intervals of up to 30 days can give excellent results, it has been found that a have separate programming for each station high level of user attention is needed if the system have multiple starts for each station is to deliver the water savings that it is capable of providing. have ‘on’ times of from one minute to four hours If you do decide to operate a controller via a soil retain several programs in memory, even when moisture sensor or with weather data, you still the power goes off and the battery runs low must set each watering station for the types of (i.e. have a ‘non-volatile’ memory) plants watered by it. You must fine-tune the allow different crop factors to be applied to system by going through the strategy suggested each station above. The whole system must be checked are able to be programmed to comply with regularly for leaks, blockages, malfunctions in the local water restrictions controller and solenoid valves, and so on. accept inputs from soil moisture sensors and real-time climatic data.There are two ways in which a smart controllercan be managed. Arguably, the simplest effectiveway is with a soil moisture sensor (above), the bestof which have a proven track record of deliveringexcellent plant quality with the least water.The other way of operating a smart controller isvia information about recent weather (air tempera-ture, air humidity, wind speed, intensity of thesun’s radiation, water evaporation rate, rain). This The Weathermatic® ‘smart’ irrigation controller isinformation is either provided on a daily basis managed by a soil moisture sensor or by a weatherfrom the nearest weather monitoring service or station that you install on your roof gutter, as shown. 7 – DELIVERING WATER TO YOUR PLANTS 81
  • 91. IT IS E A SY TO WATERPRO OF A M EDIUM -SIZED GARDEN This example uses data for Perth and Sydney. For respectively, for these types of garden areas. both cities, the average summer (October to April, Tables 14 and 15 show average amounts of water inclusive) pan evaporation (from Table 9) is about needed to supply the needs of these four different 1200 mm. The amounts of water required to types of plant communities. maintain gardens will always be lower than this. These figures show that highly drought-tolerant For this example they will range from: plants should need no extra water if rainfall for the 15% of these figures (highly drought-tolerant period is at least 180 mm. Moderately drought- species grown – crop factor 0.15), through tolerant plants should need no extra water if 30% (plants with moderate drought-tolerance rainfall is at least 350 mm. On average, – crop factor 0.3), to Perth receives just 120 mm of rain during the 40% (mixed garden with some drought- October to April period, while Sydney (airport) tolerant species, some less tolerant ornamental receives 484 mm. These amounts of rain would plants and some vegetables and fruit trees – supply, on average, 24 and 97 kL to a 200 m2 average crop factor of 0.4), and garden in Perth and Sydney, respectively. So in 80% (vigorous lawns, high-water use ornamen- Perth even drought-tolerant plants will need tal plants – crop factor 0.8). some greywater or tank water during summer. In Sydney, it is possible to have a garden of moder- To calculate the amounts of water needed for a ately to highly drought-tolerant plants with rain 200 m2 garden in Perth or Sydney, multiply only, except in years when summer rain is well 1200 mm evaporation by the 0.15, etc., crop factor below average. x 200 m2 area and divide by 1000 L/kL. The calculated amounts of water required in summer For a mixed garden in which some fruit and are 36, 72, 108 and 192 kL (1 kL = 1000 L), vegetables are being grown, all greywater and Table 14. Some figures for water inputs and use by a ‘typical’ suburban house: block 600 m2 ; house and shed 300 m2 ; paved areas 100 m2 ; garden 200 m2 . The figures are to be compared with summer water requirements (October to April, inclusive) of 36, 72, 108 and 192 kL for 200 m2 of highly drought-tolerant, moderately drought-tolerant, mixed, and lush plantings, respectively, for Perth and Sydney Rainfall Rain falling on Rain falling on during Rain falling Greywater garden plus all garden, plus all summer Rain falling on garden potentially available greywater diverted greywater, plus (mm) on roof * (kL) area (kL) for garden^ (kL) to it (kL) 10 kL from tank (kL) 0 0 0 70 70 80 100 30 20 70 90 100 200 60 40 70 110 120 300 90 60 70 130 140 400 120 80 70 150 160 500 150 100 70 170 180 * Rain falling on paved areas is one-third of these amounts. ^ From www.health.nsw.gov.au for an ‘average’ household of three people.82 GOOD GARDENS WITH LESS WATER
  • 92. Table 15. Extra water needed above that supplied by rain falling on the garden plus all greywater and 10 kL of tankwater, as listed in the last column of Table 14 (kL/summer) Highly drought- Moderately drought- Rainfall during tolerant plants tolerant plants Mixed garden Lush garden summer (mm) (need 36 kL) (need 72 kL) (need 108 kL) (need 192 kL) 0 0 0 28 112 100 0 0 8 92 200 0 0 0 72 300 0 0 0 52 400 0 0 0 32 500 0 0 0 12some tank water will be needed in both Perth and trast, larger gardens will need proportionally moreSydney. Some municipal water will also be needed water than the amounts listed here. It will bein Perth. A lush garden would need considerable increasingly difficult to maintain a garden withoutamounts of municipal water, even if all greywater municipal water as its size increases. Only with aand some tank water is used. rainwater storage capacity in the 30–100 kL rangeWaterproofing a garden becomes easier as garden might this be possible. That is the range from asize decreases in relation to house size. In con- farm-size tank up to a large swimming pool. 7 – DELIVERING WATER TO YOUR PLANTS 83
  • 93. Rain is the best. (Photo: Eleanor Handreck)
  • 94. G A R D EN WAT ER I N G S YS T E M S KEY POINTS Buckets and watering cans Hoses Hand-held and fixed sprinklers Drip systemsThere are six main types of systems for Form shallow earth walls around each ofwatering gardens: the plants you want to water, so that the bucketed water is retained where it will do buckets and watering cans the most good. You will no doubt already hand-held hoses have mulch on the soil. The plant will get sprinklers connected to hoses and moved the greatest proportion of the water if you by hand can pour the water so that it spreads under fixed sprinklers the mulch. Water retained in the mulch drip systems itself will only evaporate again. sub-irrigation (see p. 143).Buckets and watering cansBuckets and watering cans are hardly awatering system, but wherever waterrestrictions make it illegal to use any hand-held hoses, fixed sprinklers or drippers, thishighly inefficient way of watering plants maybe your only option for providing somemunicipal water to your plants.Here are guidelines which will help you get Water can be retained around young plants eitherthe most out of buckets and watering cans. with an earth dam or with a GreenWellTM . 85
  • 95. Even simpler is to allow water to slowly drip from a plastic container that has a tiny hole formed by inserting a hot needle through the side near its base. If you are not allowed to use any ‘new’ tap water on the garden, you can still provide extra water to your plants via rainwater stored in a tank or via greywater. Hand-held hosesA simple drip system for bucketed water. Note that water supply authorities require that a hand-held hose must end with a trigger If it is legal in your area, you could rig up a sprayer that automatically shuts off when you dripper system that is fed from a pail or do not hold it. Most trigger sprayers have a drum sitting on a stool. You fill the drum number of settings. Trials at the University of from a bucket and the water slowly flows to Melbourne, Faculty of Land and Food the soil under a few prized plants. Because Resources campus at Burnley (previously the drippers are designed to operate at a Burnley Horticulture College) have shown higher pressure, the drip rate will be very that on the ‘shower’ setting, the rate of water slow, but nevertheless sure. Adjustable delivery can be around 1000 mm/hr if all the drippers (e.g. Octa) will work with a low water were to go onto the same area. This is at head of water, and are easy to clean if they least 20 times the ability of most soils to become clogged. absorb water, so you must move the spray around. Unless you move systematically, the area will be watered unevenly. When this is combined with the inevitable boredom associated with hand watering, the typical outcome is that the water rarely penetrates more than a few millimetres into the soil. Repeated light sprinklings that penetrate no more than a few millimetres encourage shallow root production and are just a waste of water. In fact, all of the water can be wasted if the soil is covered with a fine mulch that retains all of the water (see p. 98). While studies in Sydney have shown that, for smallPlastic water-filled traffic barrier slowly watering alarge tree in Melbourne during the 2006–07 summer. areas of small gardens, hand-held hoses can(Photo: Geoff Connellan) be effective, this will happen in drier areas86 GOOD GARDENS WITH LESS WATER
  • 96. Trigger sprayer. Several types of micro-sprinklers.only if you apply at least 20 mm depth of switch on a number of valves in sequence,water on each occasion. starting at a time that is programmed into the controller. Each area can be separately switched on for a specified time.Sprinklers on hosesWhere they can be legally used, sprinklers on Advantagesthe ends of hoses offer more flexibility than Compared with sprinklers that have to bebuckets or hand-held hoses. The main moved by hand, they save a lot of time.disadvantage is that you need to be there to Watering is taken care of even when youshift them and turn them on. Tap timers are away from home.allow automatic turnoff. If they are well designed, they water evenly and thoroughly. Well-designed systems are the next best thing after rain.Fixed sprinkler systems Watering can be programmed for the period before sunrise when evaporationIn fixed sprinkler systems, the pipes carrying losses are lowest.the water to the sprinklers are permanently Watering can be programmed to takeinstalled in the soil or on its surface. In- account of the infiltration rate of the soil.ground installation is essential for lawns.Both in-ground and surface installation canbe used in garden beds. Micro-sprinklers that Disadvantagesspray water under trees and shrubs often give The main ‘disadvantage’ is that the use ofbetter coverage in garden beds than do larger fixed sprinkler systems is now banned infixed sprinklers, whose water can be many parts of Australia. The principalintercepted by foliage. A solenoid valve is reason given is that losses by evaporationinstalled between the mains water supply and from water droplets as they fly through thethe pipe system serving an area of the garden. air make all sprinklers more wasteful ofThis solenoid valve is connected electrically to water than are drippers. The reasoninga controller that can be programmed to apparently is that by using drippers, 8 – GARDEN WATERING SYSTEMS 87
  • 97. gardeners will use less water than if they Other considerations for sprinkler systemswere allowed to use micro-sprinklers. This is Eliminate runoff by adjusting the rate ofnot necessarily true. The Sydney survey watering to below the infiltration rate ofquoted in Table 22 (p. 118) showed that the soil. For most soils that means that themany gardeners applied much more water application rate should be less than 20 mmthan their plants needed no matter whether per hour, and for some, less than 10 mmthey delivered the water via micro-sprinklers per hour. Many older pop-up sprinkleror drippers. This was put down to poor systems deliver about 50 mm per hour.system design and lack of understanding of Their ‘on’ periods must be short andthe systems, rather than to any inherent interspersed with ‘off’ periods to allowinefficiency in them. Both micro-sprinklers infiltration. For example, you could set theand drippers can be efficient methods of controller to run the sprinklers on awatering when they are used in accordance 15-minutes-on, 30-minutes-off cycle untilwith the guidelines provided in Chapter 7. the required amount of water has beenHowever: delivered. Drippers are to be preferred over Losses can be large from some pop-up sprinklers if your water is very salty. systems whose sprinkler heads produce It is strongly recommended that if you very fine droplets and mist that is simply intend to install a fixed watering system blown away. The cause is the use of the yourself, you should have it designed by an wrong sprinkler heads and/or operation at irrigation professional, or at least have too-high pressure. The readily available your design checked by such a person. gear-driven sprinklers that operate at Poor design is a common cause of watering lower pressure and deliver medium-sized systems giving poor performance. drops are best. The combination of micro-sprinklers and a thick layer of fine organic mulch is a sure recipe for wasting water. Most of the water Drip systems will be retained in the mulch and will The key part of a drip irrigation system is a simply evaporate again (see p. 98). ‘dripper’ or ‘emitter’ from which water can If you are still able to use a fixed sprinkler flow at a slow rate. Drippers are either already system, you must: installed by the manufacturer into – regularly inspect it for leaks or polyethylene pipe or you buy them separately blockages and fix these as needed, and install them into black poly pipe yourself. The dripper line is run out across the area to – use the information in Chapter 7 to set be watered and then buried under the mulch. the controller to deliver only the The water is applied straight onto the soil minimum amounts of water needed by surface. the plants in each area, or – use a smart controller and other devices Even if you get a contractor to do the design discussed in Chapter 7. and installation for you, the information88 GOOD GARDENS WITH LESS WATER
  • 98. Some of the components of a dripper system (clockwise, from top left): adjustable solenoid valve; one type of filter; air release valve; flush valve; pressure reducer.(From top:) Netafim™ Techline™, Toro Drip Eze™. allow operating times of at least twoprovided here will enable you to interact hours and preferably up to four hours.effectively with the contractor so that the best Having long run times for clay soilspossible outcome is achieved. Where you allows you to water deeply and hence ascannot use dripper systems to deliver infrequently as a couple of times permunicipal water to your plants, you can use the summer)information to design systems for delivering solenoid valve with flow controlgreywater or rainwater. If you intend to ‘DIY’, wires to connect the controller to eachyou should still get your design checked by an solenoid valveirrigation professional (see www.irrigation.org.au for more information). in-line filter that can be easily accessed for cleaning in-line pressure reducer. The flow control on the solenoid valve may be sufficientDrip system design poly pipe containing drippers that is laidThe essential components of a drip watering out under the mulch under your plantssystem are: joiners and clips for the poly pipe a valve to allow flushing. a water supply a backflow prevention device for municipal supplies Main advantages of drippers tap timer or a programmable controller Evaporation losses are reduced compared (For dripper systems the controller must to those from sprinklers. 8 – GARDEN WATERING SYSTEMS 89
  • 99. The root zone of the plant can easily be kept near field capacity; plants therefore DRIP WATERING O F keep growing at their maximum rate. This DROUGHT-TOLER ANT is good for vegetables and fruit trees, ORNA M ENTAL PL ANTS which will produce most abundantly when A key strategy in having an attractive garden the required amount of water (see p. 72) even when the use of municipal water is severely is applied every few days. The watering restricted is to grow moderately to highly strategy must be different for ornamental drought-tolerant plants (see Chapter 2). These plants, as given in the box. plants can still look attractive with rain only, or Salts in water are washed to the outer rain plus a small amount of extra water. They do margin of the wetted zone. Therefore this in part by producing extensive root systems water of higher salinity can be used than is that penetrate deeply into the soil, and in part by possible with sprinklers. having hard leaves that still look much the same Dripper lines are easily controlled even when the plant has to ‘shut down’ because automatically. of low water supply. Towards the end of the dry Drippers are useful for difficult-to-water season in their native habitats these plants may areas such as steep slopes. have shed leaves. The remaining leaves may be pale, with a ‘hang-dog’ look. Some individuals will have died. We do not want to have thisSome disadvantages happen in our gardens, so we generally must Drippers need to be checked regularly for apply at least some extra water. blockages. You can easily waste large amounts of The least water is used by drought-tolerant water with a drip system. Use the plants if you allow them to become water- information here and in Chapter 7 to set stressed between irrigations. This is not achieved by watering them once a week via drippers. the length and frequency of ‘on’ times. Rather, they should be watered infrequently, Too few drippers per plant, especially with each application being enough to penetrate in sandy soils, will restrict root growth deeply into the soil. Where you are only able to and allow plants to be more easily blown water once a week, it would be best to rotate over. applications amongst several areas. Rather than Operating drippers under established give all plants some water each week, you use ornamental shrubs and trees in the same all of your allowed watering time for a week on way as under fruit trees will waste large one area, then on another area the next week. amounts of water (Table 10). Don’t run Watering intervals of up to four to eight weeks established ornamentals and fruit trees should generally give satisfactory results. This on the same line if you want to save strategy assumes that your soil is deep enough to water. hold within the plants’ rooting depth all of the A filter is essential if the water source is a water provided, and that the infiltration rate is surface dam or greywater and highly high enough to allow it to all soak into the soil. desirable with municipal water supplies.90 GOOD GARDENS WITH LESS WATER
  • 100. If you notice wilting on only one side of a tree or shrub that is watered via drippers, suspect that a dripper has blocked. Check and fix.Types of drippersThere are several basic types of dripper From left: two types of adjustable drippers; twosystems. non-adjustable drippers (the cap on the third from the left can be replaced with a blank cap if a dripper isThe simplest to install are those in which temporarily not needed); beneath pipe: non-drippers are already incorporated into poly adjustable dripper. All but the dripper at top right canpipe by the manufacturer. The drippers are be opened for clearing blockages.typically 30 cm apart. Two variations areavailable: pressure-regulated and regulated. While this system takes longer tounregulated. Because you probably do not set up, it is more versatile than theknow the pressure of your water supply and manufactured dripper lines for somebecause of some variation along dripper lines, applications. You can put the drippers whereit is strongly recommended that you use only you want them and leave them out whereregulated (pressure-compensating) dripper there is no need to apply water. This system islines. You should also install a pressure excellent for plants in containers and whenreduction valve. Lines whose drippers each isolated shrubs are to be watered. Drippersdeliver 1.6, 2.0 and 2.3 L/hour are available. that deliver 2, 4 and 8 L/hr are available.Some products are designed for installation Check flow rates as illustrated, or by holdingin the soil below lawns. Their drippers are a film canister (volume 35 mL) under atreated so as to prevent root entry. dripper for a known number of seconds. Alter water pressure if the drip rate is too high orIn the second main type of dripper system, too low.individual drippers are inserted into blackpoly pipe. Use only those that are pressure- Weeper hoses made from old tyres are a type of dripper system in which water leaks out allDripper line for greywater is lilac-coloured and haslarger dripper holes than ‘normal’ line. Checking flow from a dripper. 8 – GARDEN WATERING SYSTEMS 91
  • 101. along the hose. Australian trials have shown Horizontal distance (cm)that discharge rate can vary by eight-fold 0 20 40 0 20 40 60along a 9 m length. Water delivery rate can be 0very high at normal domestic water pressures.If you do decide to use them, you must check 20flow rate (use the water meter) and only water Vertical distance (cm)long enough to give the amount of waterneeded. Clogging may necessitate annual 40replacement. Sand 60 low rate high rate 0Watering patterns for different soiltextures LoamSprinklers can deliver water fairly evenly to 20 low rate high ratethe whole area being watered. In contrast,drippers put water onto the soil at separate Wetting patterns under drippers.points. Much of the water from a drippermoves straight down through the soil. Theamount that moves sideways depends on the Spacing of linestexture of your soil, the rate of delivery and In dry weather, plant roots will be gettingthe slope of the site. Typical wetting patterns most of their water from these wetted patchesare shown in the diagram. of soil. If your plants are to get enough water,Note that: the dripper lines must be spaced closely enough for the plants to get enough water There is more sideways movement of water during the chosen watering period. Here are in loam and clay soils than in sandy soils. some suggestions: Increasing application rate allows more sideways movement, especially in clay soils. For narrow beds up to about 0.5 m wide, as This is because some of the water ponds between a fence and driveway, one dripper on the soil surface and flows sideways line running the whole length of the bed is before it soaks into the soil. enough. To maximise lateral movement of water in For wider garden beds of rectangular to sands, use drippers that deliver 2–3 L/hr. square shape, run two or more parallel Delivery rates for loams should be in the lines of drippers. Have the dripper lines 1.5–2.5 L/hr range and for clays 1–2 L/hr. This means that to supply the same 20–25 cm apart on sands, 30–50 cm apart amount of water per unit area of soil, on loams and 40–70 cm apart on heavier delivery times will be shorter for sands soils. than for heavier soils. Use the information For garden beds of irregular shape, either in Chapter 7 to work out ‘on’ times. run parallel lines in the middle of the area92 GOOD GARDENS WITH LESS WATER
  • 102. An installation of the Irritrol Drip-In™ system under a Adjustable drippers are needed for containers.new lawn area. Each dripper has been impregnatedwith a tiny amount of the herbicide Treflan. Long-termuse in the USA has shown that roots are excluded for Run times for drippersat least 18 years. Drippers should be run only for the length of time that will deliver the required amount of and fill in around the edges, or roughly water to the area, as calculated with the follow the shape of the bed. information provided in Chapter 7. The For fruit trees and isolated trees set in general guidelines are: lawns, run circles of dripper line around each tree, out to the edge of the foliage if For fruit trees, run the drippers each week possible. during summer. For bedding plants and vegetables, run For ornamental plants of moderate one or two dripper lines along each row of drought tolerance, run them every two to plants. Using two lines allows you to three weeks for times calculated with a stagger the drippers so that you can have crop factor (see p. 75) of about 0.45. the plants closer together. Space lines no For drought-tolerant plants, run them more than 20 cm apart. every four to eight weeks for times calculated with a crop factor of about 0.2.Line length per runThe low rate of delivery of water from eachdripper means that you can have quite longdripper lines. The maximum number ofdrippers that can be run depends on waterpressure, pipe diameter and dripper rating.For operation within the designed waterpressure range of 50–400 kPa, you can run upto 100 m of 1.6 L/hr drippers in 13 mm pipeand up to 75 m for 2 L/hr drippers. You would This Beaucarnea recurvata (Ponytail Tree) is easilyprobably not exceed a quarter of these lengths maintained in a large planter bed via a circle ofwhen all the drippers are rated at 8 L/hr. dripper line. 8 – GARDEN WATERING SYSTEMS 93
  • 103. For containers of 1–4 L capacity, one dripper per container will be enough. There are two options for larger containers: – have one dripper each side of the plant stem, or – have a circle of dripper line around the stem, where more than two drippers are needed. Dripper lines among decorative potted plantsYates Tuscan planters have a built-in water well. are fairly ugly. An alternative that minimises watering effort is to use pots that include water wells that can supply water for up to aDrippers for pot plants month.Here is some essential information to ensurethat you can successfully use drippers to waterplants in pots: The very open nature of good potting mixes means that there is only limited sideways movement of water. You need to either have some means of spreading out the water across the surface of the mix or you need to use more than one dripper per container. So that you do not waste water, use adjustable drippers so that you can regulate the amount of water being One of the extensive range of ‘self-watering’ planters applied to each container. from The Container Connection.94 GOOD GARDENS WITH LESS WATER
  • 104. M U LC H E S : T H E FAC T S KEY POINTS Myths about mulches Facts about mulches Where to use organic and inorganic mulches Coarse mulches are bestMulch is a layer of material on the surface of composts, cereal straw, pea straw, bagassea soil. A mulch may consist of: (sugarcane mulch) and so on. a layer of inorganic material such as scoria, some of the soil itself. The dry upper part gravel, water-worn pebbles, crushed of a gravelly or sandy soil is an excellent lateritic rock (WA) or crushed bricks. mulch. Some clay soils self-mulch as they dry out. Light raking of other soils after every rain or irrigation can create and maintain such a layer. Myths about mulches organic materials such as wood chips, Myth 1. Organic mulches should be spread chunky pine bark, green organics around all garden plants and to depths of 70– 100 mm. Many gardening books, retail packs and most water authority websites make this sort of recommendation. The factual information provided on the next few pages will show you that this is not universally sensible and, for some organic mulches, is totally silly. Myth 2. Organic mulches will reduce water loss from a garden by up to 70%. While it can be true that a dry organic mulch will reduceLoose surface soil makes an excellent mulcharound this Wreath leschenaultia in inland evaporation from moist soil below it by 70%,Western Australia. the plants growing in the soil will still be 95
  • 105. Maybe not everyone’s idea of a colour scheme. transpiring water. Factual data for Sydney show that organic mulches reduce total water use in a garden by no more than about 10%. That can, of course, be very useful when water restrictions are severe. But note other facts below about the interaction between organic mulches and rain. Myth 3. Mulches are improved by the addition of a wetting agent. Mulches and water A main benefit provided by mulch to gardeners and their plants is its ability to reduce the loss of water from the soil. The way mulches do this is much the same as the way a blanket keeps us warm at night. The layer of still air within the blanket slows down the movement of warmth from our body to the general atmosphere. The layer of still air within a mulch slows down the movement of water vapour from the soil surface to the air above. You might think therefore that the thicker aOrganic mulches (from top): coarse pine bark, hoop mulch, the greater the reduction in waterpine bark, chipped wood in three colours. loss.96 GOOD GARDENS WITH LESS WATER
  • 106. Some mulch bags have sensible instructions … … others do not. If only life were that simple. Mulches are much more complicated than that. The main complication is their interaction with rain. Mulches hold water. The thicker a mulch, the higher will be the proportion of any rain that is retained. This water does not reach plant roots in the soil below. Here are some guidelines from research on organic mulches.Inorganic mulches (from top): three types of water-worn stones, crushed rock, crushed bricks. Coarse wood chips make an excellent mulch. 9 – MULCHES: THE FACTS 97
  • 107. Water held by organic mulchesAs shown in the next two tables, fine mulchesto which a wetting agent has been added canretain large amounts of rain.Table 16. Effect of particle size on rain held by wood chip Actually, moisture retentive mulch is not what youmulches need. Rain held by 35 mm thick mulch (mm) water provided by a rain event or sprinkler Particle size Water-repellent Wetting agent range (mm) mulch added to mulch application of up to 42 mm! >12 2.5 2.7 A 100 mm thick layer of fine mulch that 6–12 3.0 3.0 has had a wetting agent added to it could 5–6 3.1 3.3 trap up to 60 mm of rain or sprinkler 2–5 5.3 7.1 water before any water reaches the soil. Where rain falls as infrequent light showers,Table 17. Effect of fine particles on rain held by wood chipmulches fine organic mulches will prevent all rain from reaching the soil below. Percentage of Rain held by 35 mm thick mulch (mm) particles Mulches with high proportions (greater than smaller than Water-repellent Wetting agent 2 mm mulch added to mulch 80%) of particles larger than 5 mm are best at 30 4.9 5.3 letting rain reach the soil below them. But 50 5.8 8.1 how do they perform in reducing 70 7.7 18.6 evaporation? The next two tables give 75 8.6 21.1 information for the mulches listed in Tables 16 and 17.These tables show that: Table 18. Effect of mulch particle size distribution on water loss from moist wood chip mulches Mulches whose particles are all larger than Water lost from water-repellent 5 mm retain only modest amounts of rain. mulch for the first six days after rain Particle size (mm) Wetting agent has little effect on the range (mm) 35 mm deep 70 mm deep amount of water held by them. >12 4.6 4.3 Any inclusion in the mulch of particles 6–12 4.1 4.5 smaller than 5 mm increases the amount 5–6 3.6 3.9 of water held. However, if the mulch is 2–5 3.0 3.6 water repellent, the increase is modest. Unmulched soil lost 11.8 mm. Mulches with high proportions of easily wet This table shows that: fine particles hold large amounts of water. According to the figures given above, a For the coarse mulches (all particles larger 70 mm thick layer of fine mulch, as is than 5 mm), changes in particle size widely advocated, could hold all of the distribution had little effect on water losses.98 GOOD GARDENS WITH LESS WATER
  • 108. Doubling mulch thickness for these coarse the mulch is initially dry and irrigation is via mulches did not reduce water losses, so drippers placed beneath it? Here is some with these coarse mulches there is no information. need to spread them any deeper than Table 20. Effect of particle size on losses of water through 35 mm. dry, water-repellent organic mulches sitting on constantly moist soilTable 19. Effect of fine particles and wetting agent on water Water lost (mm) through water- Percentage ofloss from moist wood chip mulches repellent mulch 35 mm deep particles smaller Water lost from 35 mm deep mulch than 2 mm First week Second week Percentage of particles in the first six days after rain (mm) 0 7.3 6.8 smaller than Water-repellent Wetting agent 10 7.5 7.3 2 mm mulch added to mulch 30 7.1 7.4 30 7.0 7.4 50 7.1 7.5 50 7.4 9.2 70 10.9 12.7 70 7.7 17.7 75 11.1 12.6 75 7.8 19.1 Control (no mulch) 17.5 18.2 Unmulched soil lost 14.5 mm. Shaded cells: water loss was greater than from unmulched soil. This table shows that:This table shows that: For water-repellent mulches, only those mulches with high proportions of fine As the proportion of fine particles particles have higher rates of water loss increases, losses of water from the water- than have coarser mulches. repellent mulch changed little, but The best (coarse, water-repellent) mulches increased greatly when wetting agent had reduced water loss by up to 63% been added to the mulch. ((18.2 – 6.8) 100 ÷ 18.2). The worst As the proportion of fine particles in a (finest) only reduced it by about 40%. water-repellent mulch increases, water loss increases only slightly. This is because the Table 21. Effect of particle size on losses of water through particles at the surface of the mulch dry out dry, water-absorbing organic mulches sitting on constantly moist soil and so act as a mulch on top of the mulch. Water lost (mm) through mulch But when the mulch has had a wetting 35 mm deep that had been Percentage of agent added to it, water loss increases particles smaller treated with wetting agent than 2 mm First week Second week greatly as the mulch becomes finer. This is 0 8.5 7.2 partly because these mulches hold much 10 7.8 6.6 water, but they also allow water to wick up 30 8.9 6.7 through them from the soil below, as is 50 9.8 7.0 shown in the next tables. 70 20.3 19.3 75 21.6 19.8So far the tables have been about the Control (no mulch) 17.5 18.2response of mulches to water from rain or Shaded cells: water losses were greater than from the unmulchedsprinkler irrigation. What are the losses when soil. 9 – MULCHES: THE FACTS 99
  • 109. This table shows that: If we follow this line of reasoning, a useful technique for a soil that has little organic When a mulch is easily wet, a high matter in it would be to first spread fine proportion of fine particles allows the mulch or soil conditioner over the soil and mulch to actually lose water at a faster rate then top it with coarse mulch. than bare soil (shaded areas of the table). There is no need to spread them to a These mulches are in fact anti-mulches. depth of 70–100 mm as is often advocated. Some mulches sold in retail packs are A 50 mm thick layer is enough. like this. The finer the mulch, the shallower should These fine mulches lose water rapidly be its depth. Fine mulches spread deeply because they allow capillary rise of water will prevent much rain from reaching from the soil below. Many of the spaces in plant roots and may even increase water these fine mulches are filled with water, so loss from the soil below. there is no still air to break the contact They are best if they are water repellent. between water in the soil and the Including a wetting agent in fine mulches atmosphere. causes them to retain a high proportion of rain or sprinkler water and also allows them to suck water out of the soil.Conclusions for organic mulchesThe main take-home messages for organicmulches are: Other very important facts about They should have more than 80% of their organic mulches particles larger than 5 mm and very little Natural ecosystems have a very wide range of dust. These coarse mulches simulate the amounts of leaf litter (mulch) on their soils. litter on a forest floor. There, the coarse, Here are some comments for specific recently fallen leaves, branches and twigs ecosystems: sit on top of earlier falls, which have At one end of the range are desert areas become finer as small animals and where cacti and succulents grow. Rocks are microbes have used them as food. the main, and highly effective, ‘mulch’. This suggests that organic mulches should not be spread under such plants. In fact, research has shown that applying organic matter actually harms these plants. Even in the less harsh areas where other drought-tolerant plants grow, the litter layer (mulch) on the soil surface is generally quite sparse. In gardens, these plants might benefit from a thin (25 mm)Natural mulch under ferns, Lord Howe Island. layer of wood chips or other coarse organic100 GOOD GARDENS WITH LESS WATER
  • 110. Other important facts to note are: Fine organic mulches made from thoroughly composted materials will not contain weed seeds, but they do make excellent seed beds for any weed seeds that blow in. Weeds are less of a problem with coarse mulches. Strong positive effects are seen when fruit trees and vegetables are mulched with nutrient-rich organic materials. Natural leaf litter is very low in plant nutrients. Plants remove most nutrients before they shed leaves. If you apply organic mulch that is rich in plant nutrients, especially nitrogen and phosphorus, to drought-tolerant plants, you will over-stimulate them and so reduce their ability to cope with drought. Reserve these high-nutrient mulches for fruit trees and vegetables. Application of thick layers of organic mulch to drought-tolerant plantsGravel and loose sand are the mulches of dry areas(from top): Stylidium elongatum in south-western encourages their roots to grow up into theWestern Australia, Didierea madagascariensis in lower part of the mulch. What is reallysouth-western Madagascar. needed is to encourage them to grow roots deep into the soil by infrequent deep matter during establishment, but natural watering, or just leaving it to rain. leaf and twig drop after that should be all Observation in environments from central that they need. Queensland to Victoria has shown that no In the native high-rainfall habitats of many harm is done to trees and shrubs when cool-climate, drought-sensitive plants, the coarse mulch of maximum desirable soil surface is covered with a thick layer of thickness (up to 50 mm) goes right up to organic matter. For their best growth in their trunks. Maybe the injunction to keep gardens, they need to be provided with organic mulches away from trunks is similar amounts of organic matter, but of sensible for thick layers of fine mulches in course in areas of lower rainfall than the constantly wet environments. native habitat, thick, fine mulch will Snails and slugs shelter and breed in probably prevent almost all rain from organic mulches. Use traps or baits to reaching the soil. eliminate them. 9 – MULCHES: THE FACTS 101
  • 111. Snails like the beer used to bait this snail trap. In bushfire-prone areas, organic mulches may contribute to fire intensity.Extra comments on organic mulchesWoody organic mulches such as pine bark(composted or not), wood chips (colouredand natural), chipped tree branches andscreened composted green organics will lastfor many years. Crop residues such as cerealstraw, pea straw, sugarcane residues and baled Living alternatives to mulch (from top): small Minurialucerne will last for only one season, so they daisy bushes and Carpobrotus modestus (Inlandare useful for mulching annual crops such as Pigface). (Photos: Eleanor Handreck)vegetables. Pelleted organic materials usuallyfall apart to give a very fine mulch. Do not use: anything that is likely to attract flies wood chips from diseased trees and shrubs diseased wastes, such as the remnants of tomato and zucchini bushes at the end of a growing season pure lawn clippings or autumn leaves (because they pack down into a dense matSugarcane mulch. that allows little water to reach the soil).102 GOOD GARDENS WITH LESS WATER
  • 112. Either compost these to make soil suppressing weeds. They look best when improve or mix them with coarser covered with a coarse organic mulch. materials such as chopped tree prunings Never use plastic sheeting, because it will not and corn stalks only prevent all rainwater from reaching the sawdust (because it will retain a high soil but will also prevent vital oxygen from proportion of water from light showers and reaching plant roots. In summer, the high so reduce the amount reaching plant temperature under it will cook roots. roots).Ground cover plants act as a living mulch.They will of course transpire water, but they Other effects of mulchesdo reduce water loss from the soil itself by Besides their potential to reduce water lossshading and acting as a blanket. But don’t use from soils, mulches have other worthwhilethem where their water use will rob water effects in our gardens. They:from plants that have greater need for it. protect the soil surface from heavy rain, and so reduce the risk of crusting and erosionNon-organic mulches slow the flow of water across the soil and soThe main non-organic mulching materials increase the proportion moving down toare: where roots can use it minerals such as pebbles, gravel and change the temperature of the underlying crushed bricks. These are used mainly to soil. Organic mulches keep the soil cooler give interesting visual effects in smaller than it would have been without a mulch gardens. They can be excellent at help control weeds (provided that the minimising water loss, but have the organic mulches do not themselves contain disadvantage that their exclusive use can weed seeds) impoverish the soil beneath them if fallen keep the fruit of crops such as strawberries leaves and twigs are removed from them. and cucumbers off the soil and so clean Another disadvantage is that weeds that and less liable to disease germinate amongst them are difficult to improve soil structure as they decompose, remove. It is best that they be used mainly if they are readily decomposable organic in dry areas or under highly drought- materials tolerant plants such as cacti and provide nutrients as they decompose. But succulents. note the comment above about decrease in woven plastic materials such as weed drought tolerance caused by some of these control mats. These can be useful for nutrients. 9 – MULCHES: THE FACTS 103
  • 113. Therese Scales, Tikalara Designs, Victoria
  • 114. NEW GARDENS AND NEW GARDENS FROM OLD KEY POINTS Seek help from a garden designer and a qualified landscaper For new homes: Planting for success Soil blendsNot so long ago, new gardens were usually If you are employing a garden designer, he orcreated through the efforts of new home she will have arrangements with competentowners themselves. Over months and years, as landscapers. Positive recommendation bythey found the money and time to do it, they friends who are very satisfied with the jobgradually converted their block into a garden. done by a contractor is another good guide toGardeners also tended to do renovations the competence of a landscaper. If none ofthemselves. Many gardeners now do not have your friends or acquaintances has this sort ofthe time or energy to undertake these major information, your next source will be one ofjobs. Perhaps under the influence of the the professional associations that cover the‘instant makeover’ television shows, many landscaping and urban horticulturehome owners now employ a landscaping industries. These are: the Australian Institutecontractor to do the work. But how do you of Horticulture; the Australian Institute ofchoose a competent landscaper? Your Yellow Landscape Designers and Managers; thePages lists dozens to hundreds of contractors. Landscapers Association of your state; theWhich ones are competent? The ones with Nursery and Garden Industry Association ofthe biggest ads or the most interesting names? your state; the Australian Society of GardenHere are some suggestions. Designers and the Australian Institute of 105
  • 115. Landscape Architects (see Appendix 1 for a on the roof and the greywater generatedlist of their websites). Associations require within the house (see Chapter 7 fortheir members to have formal horticultural information about rainwater tanks, andqualifications (certificate, diploma or degree) Chapter 6 for greywater). The ultimate inand to have proven their ability in their water-proofing your home is to build in waterparticular fields. storage under paved areas and patios (see p. 68). The landscape designer would helpBut also be aware that some competent you design the paved and garden areas so thatpeople have chosen not to belong to an the runoff from the paved areas provides theassociation. Rather, they rely on the greatest benefit to the garden.considerable reputations they have earnedthrough excellent work that is publicised by Also use a design that has no small areas ofword of mouth from those who have garden. They are hard to water efficiently.benefited from their skills. The Sydney study quoted in Table 22 (p. 118) showed that small areas often received fourWhatever you do, be wary of quotations that times the water needed by the plants growingare considerably lower than all others. You there.will get what you pay for. Excellent results callfor the use of excellent materials that areinevitably more expensive than inferiormaterials. A quotation that is low because it Save the topsoilspecifies a shallower layer of or cheaper For a new garden, wherever possible have thetopsoil than higher quotes must be topsoil scraped from the area to be occupiedparticularly suspect. by the building and any area that will be contaminated with mortar and concrete residues during building operations.New homes: Start at the beginning Stockpile this soil elsewhere on the site for later re-use as topsoil. This soil will usually beIt is strongly recommended that you engage much better than anything you can buy fromyour garden designer and landscaper before anew house is started. Have them visit the baresite and let them become involved right fromthe start of the planning process. Then yourgarden will have the best chance ofenhancing your home.Build in water recyclingAn essential consideration is to include in thedesign ways of diverting to the garden as Being sensible: stockpiled topsoil being spread backmuch as possible of the free water that falls over formed subsoil.106 GOOD GARDENS WITH LESS WATER
  • 116. a landscaping supplies yard. A little Planting trees and shrubsmodification based on a soil analysis and help The following comments apply both to newfrom a soil scientist will give you an excellent gardens and to older ones being renovated.growing medium for your plants. The cost of Some simple precautions taken when plantingabout $200 for the analysis and trees and shrubs will greatly increase therecommendations will be much less than the chance that a plant will survive and thrive.cost of buying in a soil blend of perhapsindifferent quality. Tree quality You will of course choose a tree whose topWhat must be done by your looks healthy, but there are two other factorslandscaper that you must consider.To assist you in your interaction with your One is the quality of its trunk. The trunklandscaper, here is a list of the sorts of things should be thick and robust enough for the treethat they need to do for you: to stand erect without the aid of a stake. Trees Clean the site. Remove debris and weeds. with thin trunks that have to be staked are Remove soil that is heavily contaminated easily damaged during and after planting out. with mortar and concrete washed from An even more important factor is the quality builders’ tools. of the root system. You cannot go around a Relieve, through ripping, the compaction nursery extracting semi-advanced and that will have been caused by the advanced trees from their containers to look movement of construction machinery over at their roots, but you can get an idea of what the soil. they might be like. Trees grown in round Grade and contour the area before the plastic pots often have roots circling around topsoil is spread back. If necessary, the outside of the root ball. This does not before forming the final grades, happen if the inside walls of the pot have temporarily remove topsoil from any area been sprayed with copper hydroxide solution. in which it was left intact during house You can see this as a light green film on the construction. inside of the pot. The copper kills the tips of Test the drainage of the formed subsoil, as roots that come into contact with it. This shown in the box on the next page. prevents circling of the roots, but it also forces Thoroughly mix any layer of coarse sandy prolific branching of roots within the root material with the soil above and below it. ball. See p. 109 for another option. If necessary (see p. 36), add gypsum. Have the stockpiled topsoil tested and amended as is indicated by the analytical Time of planting results. Restrictions on the use of municipal water Spread the amended topsoil over the now dictate that trees and shrubs should be contoured subsoil. planted as early as possible in the rainy 10 – NEW GARDENS AND NEW GARDENS FROM OLD 107
  • 117. M E A SURING THE INFILTR ATION R ATE O F A SOIL For soil at the surface Area of base: 3.142 x 13 x 13 ÷ 10 000 = Cut a hole of 6–7 cm diameter in the bottom of 0.0531 m2. an old, thin-based, aluminium saucepan of Volume of water lost from the second flagon: 20–26 cm diameter (from a thrift store), as shown. 2.0 L. Remove the handle(s). Sit the inverted saucepan on the soil surface. Place a short piece of wood Time taken: 3.5 hours. on top of it and hit the wood with a hammer until Therefore the infiltration rate of the soil is: 2.0 ÷ the inverted saucepan has evenly penetrated (0.0531 x 3.5) = 10.8 mm/hour. about 5 cm into the soil. Invert a 2 L flagon of water into the hole in the saucepan. Much of the For a deeper soil layer water will quickly flow onto the soil surface Water movement into deeper subsoil can be within the saucepan. If all 2 L of water flows out checked by digging a hole 15 cm deep or just to of the flagon, remove and refill it and again invert the surface of any layer of clay in the subsoil. Hit it into the hole in the saucepan. When the flow the saucepan into the soil at the bottom of the has stopped, quickly remove the flagon and refill hole and proceed as described above. it. Invert it into the hole again and record the time Interpretation guidelines are given on p. 47. it takes for the whole 2 L to flow out. If this looks like taking longer than a few hours, you could remove the flagon after, say, four hours and measure the amount of water remaining in the flagon. Calculate the amount of water lost from this flagon. Calculate the area of the base of the saucepan using the formula: 3.142 x radius in cm x radius in cm and divide the number obtained by 10 000 to get the area in square metres. Then divide the volume of water (in L) lost from the flagon by the area of the base. The number you obtain is the number of mm depth of water that soaked into the soil. Finally, divide this number by the number of hours that it took for this water to soak into the soil to give the number of mm of water that would soak into the soil in one hour. Example Simple equipment for measuring the infiltration rate Radius: 13 cm. of a soil.108 GOOD GARDENS WITH LESS WATER
  • 118. The roots circling around the left root ball must be cutif the tree is not to end up like that on the right, which Advanced trees have particularly good root systemswas choked to death within three years of planting. when they have been grown in Rocket®Pots and similar containers with multiple holes in their sidesseason. That could be early to mid-autumn in and bases. When roots grow into these holes, theirsouthern Australia and early summer further tips die through dehydration. This death produces prolific formation of fibrous roots within the root ball.north. Planting at these times allows rain todo most of the early watering for you. The that is essential for their survival during theplants’ roots will have the longest time first summer/dry season.possible to establish the extensive network The planting hole Ensure that the soil surface surrounding the planting hole is free from weeds to a distance of 40–50 cm. Keeping the area weed-free and mulched is essential if early tree growth is to be rapid. The soil must be moist before planting. Dig a hole of a depth such that the top of the root ball is at the final soil height. Planting the root ball deeper than this often damages or kills young plants. The hole diameter at the soil surface mustA kinked root like this can jeopardise a tree’s be at least three times that of the root ball,longevity. Your best guarantee that this fault is not tapering to about twice this at the base.present is to source your trees from a nursery This allows good lateral root growth.association accredited nursery. These nurseries havequality control systems that ensure excellent root Loosen the soil around the hole if it issystems at every stage of production. compacted. 10 – NEW GARDENS AND NEW GARDENS FROM OLD 109
  • 119. A warning – if, when you are digging a planting hole you find that you are digging into very heavy clay that looks as if it drains very slowly, you must not plant without checking the infiltration rate by the method given above. Digging down a bit deeper may allow you to break through into more permeable soil below. If not, you will need to plant into soil mounded above the current soil surface, or you will need to provide drainage from each planting hole to a lower level. In any such area, citrus Circling roots must be cut either with a knife or, for must always be planted on a mound. larger root balls, with a spade. This attention to circling roots is less criticalPreparing the plant with shrubs than it is with trees, but major Remove all roots protruding through holes circling roots must still be cut. in the pot or tube. Just before planting, soak the root ball so that it becomes thoroughly wet. Include Planting and after-care wetting agent in the water (1 mL Bury a fertiliser ‘pill’ or two tablespoons of concentrate per litre of water) so that controlled-release fertiliser in the soil in the root ball is easy to rewet should it the bottom of the planting hole. Do not do become dry. this when planting phosphorus-sensitive Remove the pot or tube. plants (see Phosphorus Supply on p. 26).Examine the outside of the root ball. If the If necessary, put some soil back into theroots generally run straight from top to hole to ensure that the top of the root ballbottom, or have been tip-pruned by copper or is level with the intended soil surface.air-pruned, there is no need for further For small plants – those in tubes and inaction. But for young trees, any roots that arecircling around the outside of the root ball pots up to 20 cm – add into the hole amust be either cut through or pulled from slurry that contains half a teaspoon ofthe root ball. Use a spade to cut off the lower water crystals in 0.5 litre of water (soak theseveral centimetres of large root balls. Make crystals for two hours). Water crystals willseveral vertical cuts into the root ball to cut give greatest benefit in sandy soils andother circling roots further up the root ball. when frequent application of water is notFailure to remove circling roots will condemn the possible during the first two weeks. Usingplant to death in three to six years, either because it water crystals is less necessary if you canis easily blown over or because the enlarged circling apply water daily during the first two weeksroots will choke it to death. after planting. Research results from110 GOOD GARDENS WITH LESS WATER
  • 120. An earth basin is the best way of ensuring that a youngplant gets water where it needs it. (Photo: Mt WilliamAdvanced Tree Nursery) Florida suggest that water crystals are of little use when establishing advanced trees. Competition from weeds will ensure very slow Never add dry crystals to the backfill soil. establishment of a tree. As they expand during wetting, they can push the plant out of the soil. How often you apply water depends on the Lower the root ball into the slurry in the weather. For small plants with water centre of the hole. crystals in the planting hole, no extra may Add about one-third of the soil back into be needed during the rainy season. At the space around the root ball. Mix this drier times of the year and for larger soil into the water crystal slurry and gently plants, it is desirable to apply water every firm it around the root ball. Add the rest several days for the first few weeks. This of the soil and gently firm. water should be run directly into the Smooth the new soil surface to the same planting basin, under the mulch. Water level as the top of the root ball. stress is the main cause of death in newly Form a basin around the planting hole so planted shrubs and trees. that water applied to the young tree does Shrubs need no staking. Nor should trees not run away. that have robust trunks, unless they are Add more water to settle the soil in around planted into a very windy situation. If the root ball. staking is needed, knock two stakes into Apply mulch out to at least 40–50 cm from the soil outside the root ball. The trunk the trunk. should be loosely held to each stake with a loop made from soft cloth. 10 – NEW GARDENS AND NEW GARDENS FROM OLD 111
  • 121. CHO OSING A SOIL BLEND Soil blends available from soil yards are mainly some lime present. Such a soil will be suitable mixtures of fine sand or loamy sand and compost- for many garden situations. ed green organics. Some may also contain some Check to see if it is sodic (see p. 36). loam or silty loam. Because these blends often If it is, you will need to add gypsum. contain no more than a few per cent clay, they do Any blend that contains large chunks of wood not develop good structure as do natural soils. As or tree bark, especially if it looks raw and the organic matter breaks down, these blends under-composted, should be rejected. often become water-repellent, hard-setting sandy Prefer a blend whose texture is in the range loams. Their level of available water (Table 3) sandy loam to loam. The presence of some tends to be fairly low. clay in the mixture will allow it in time to develop a normal soil structure. The clay will Ask your landscaper to choose a soil blend along also allow better retention of humus. the following lines: These tests will take a little time, but nowhere Ideally only buy a blend that complies with the near as much as is needed to correct problems Australian Standard for Soils for Landscaping caused by purchase of poor soil. Be assertive: and Garden Use. Production according to this don’t be talked into accepting assurances of Standard guarantees reasonable quality. If you quality at face value. Check! cannot get a Standard product, you or your landscaper need to do some testing of a soil blend before purchase. Check its pH, to make sure that it is not too acid or too alkaline for the plants you want to grow. If its pH is above 8, you should try to get some idea of its total lime content. If you get very vigorous fizzing when a few drops of hydro- chloric acid (pool acid) are placed on it (due to the release of carbon dioxide as the lime is dissolved by the acid), the product has a high (and perhaps unacceptable) lime content. A small amount of fizzing indicates that there is Fizzing = limestone in this soil blend.112 GOOD GARDENS WITH LESS WATER
  • 122. DEALING WITH TO O M U C H WAT ER KEY POINTS Protect your soil against erosion Preventing and overcoming waterloggingGardeners in much of Australia might wonder You can do no more than clean up if yourwhat ‘too much’ water is, as there does not area is inundated, but there are a few thingsseem to be such a thing anymore. But the you can do to minimise local problems.predictions of climate scientists are that we ‘Too much’ water can cause problemswill have wilder swings in weather, so that through:there will sometimes be destructively heavyrainfall events, as there were in the Hunter soil erosionValley and East Gippsland in June 2007, even waterlogging of the soil.though the long-term trend is to increaseddryness. In contrast, prolonged heavy rain ispredicted to be more frequent in the tropics. Soil erosion Erosion is the process of removal of particles from a soil surface by wind or water. Erosion by water is prevented or reduced by: maintaining a full cover of plants so that the soil is protected from the pounding of raindrops and is held together by a mass of roots allowing water to spread in thin sheets rather than being concentrated intoBare cultivated soil plus rain = massive erosion. narrow streams of destructive force 113
  • 123. Plants announce their suffering from waterlogging by wilting, appearing stunted, looking yellower than normal and/or with the margins of the oldest leaves sometimes developing dark spots. With prolonged waterlogging there will be loss of leaves and death of root tips or whole plants. Plants whose roots have been damaged by waterlogging may look normal enough during cool weather, but will rapidly die during the first days of heat in spring or summer, when water supply to the leaves from the almost non-existent root system will not be able to keep up with transpiration. If some of your plants die during the first warm weather,Terracing is essential on steep slopes. suspect that the real cause was earlier waterlogging, whose cause should be found terracing sloping sites and corrected before you replant the area. protecting areas of temporarily bare soil You need to take action if your soil: – as when planting vegetables – with an organic mulch or with shadecloth. Water has a continuously wet surface flowing from upslope should be diverted has moss and/or slimy algae growing on its to where it can benefit plants, or to the surface street water table kills or maims your plants in wet weather improving soil structure (see Chapter 3) so has a smell of rotten egg gas when you dig that water entry into the soil is rapid. into it has free water at less than 30–40 cm below the surface.Waterlogging of the soilA soil is said to be waterlogged if most of itspores are filled with water. There is no roomfor air and its vital ingredient oxygen, whichis needed by all plant roots. Shortage ofoxygen puts stress on plant roots. This eitherkills the roots directly or it makes them moresusceptible to attack by pathogens such asphytophthora and pythium. The roots ofplants that need excellent drainage can bekilled in one day of waterlogging. Moss in a lawn can indicate poor drainage.114 GOOD GARDENS WITH LESS WATER
  • 124. Overcoming and preventing deep heavy clay that cannot be improved,waterlogging or shallow depth to bedrock, raised gardenFind the cause of the waterlogging. If it is due beds need to be constructed.to: drainage from upslope, this needs to be intercepted and the water led to where it will not cause problems. A surface drain filled with gravel may be all that is needed. an impermeable layer in the soil, this needs to be broken through or, if this is not possible, a drainage system has to be installed. You need to consult a specialist drainage contractor for this. poor soil structure, this needs to be improved (see Chapter 3). Plastic drainage pipe. 11 – DEALING WITH TOO MUCH WATER 115
  • 125. Succulent lawn.
  • 126. L AW NS KEY POINTS You can still have a lawn even when water restrictions are severe The grass must be suited to your climate and soil For most areas, choose a warm-season grass Prepare the soil thoroughly When to establish a lawn Watering lawns during drought Effects of mowing and fertilisers on water useMost Australian water supply authorities water than is needed by a bed of moderatelyencourage home owners to reduce the drought-tolerant shrubs (see Table 10, p. 75).amount of lawn they have. The main reasongiven is the fact that some of the water A recent study found that average waterdelivered to them via sprinklers is lost by applications per square metre to garden bedsevaporation as it flies through the air. in Sydney were double those to lawn areas onGardeners are encouraged to replace lawn the same property (see Table 22). There arewith beds of other plants that can be watered no figures for other urban areas, but thevia drippers. The assumption is that such difference will probably be less wherebeds will need less water than will a lawn. Is summers are much drier than they usuallythis factual? are in Sydney.One fact is that any area of well-watered But irrespective of these facts, the use ofplants – lawn or otherwise – will lose water at sprinklers on lawns is now widely bannedabout the same rate under the same climatic across south-eastern Australia. In some areasconditions. When water supply is less, a lawn there is either a total ban on watering lawnsof deep-rooted, drought-tolerant grasses can or they can be watered only by bucket orhave an acceptable appearance with no more watering can, or via buried drippers. 117
  • 127. Table 22. Average application of water by 50 Sydney Choosing the best lawn grass forhouseholders to three different types of vegetation(Maheshwari B (2006). CRC for Irrigation Futures, Tech. your areaReport 01/06) You will choose a grass that is adapted to your Monthly water climate. The many grasses that can be used applications by Type of vegetation householders (L/m2 )* for lawns can be placed into two groups. The Lawn 43 so-called cool-season grasses grow mainly in Exotic plants and some 87 the cooler part of the year; warm-season vegetables grasses grow mainly or only in the warmest Mainly native plants, some 47 exotics and hottest parts of the year. *Householders were allowed to use all types of watering systems. The biggest practical difference between cool-season and warm-season grasses forIs this the end of the home lawn? Not drought-affected gardeners is that the warm-necessarily. It would be sensible to eliminate season grasses are much more efficient thanlawn that is heavily trafficked, heavily shaded, the cool-season grasses in their use of water.in long narrow strips, of small area or just The trial results in Table 23 show that, forplain ugly. You might also find that a bed of continued satisfactory appearance,mixed shrubs is more interesting to look at infrequently watered warm-season grassesthan the monoculture of a lawn. But it is need only half the water used by cool-seasonpossible to have some lawn for children to grasses.play on, despite water restrictions. To achievethis you must use drought-tolerant grassesthat are suited to your soil and climate. With Cool-season grassesthem, you can have a reasonable lawn usingrain, supplemented a few times each summer As the name suggests, these grasses comewith greywater or water from a tank. This from areas where the climate is cool, andchapter shows how this can be done. generally fairly moist. Most of the cool-season grasses that have traditionally been used for lawns in southern Australia have come from northern Europe and eastern North America. Here are a few facts about them. Imported cool-season grasses These are all C3 grasses (see p. 17), so they are quite inefficient at using water. Tall fescue: Tall fescues are more drought- tolerant than are other imported cool-This grassed area could be made into something more season grasses, but only because theirinteresting. roots penetrate more deeply into the soil.118 GOOD GARDENS WITH LESS WATER
  • 128. Table 23. Warm-season grasses use much less water than cool-season grasses Cool-season grasses Warm-season grasses Tall fescue Kentucky bluegrass Couch grass Buffalo grass Watering frequency Water used, as a percentage of that used by frequently watered tall fescue Very frequent 100 96 69 61 Moderately frequent 90 84 57 50 Infrequent 83 78* 49 49 * All the grasses except the infrequently watered Kentucky bluegrass had a satisfactory appearance. They are still greatly inferior to the warm- Cool-season native grasses season grasses in drought tolerance. Research that started in the 1980s has finally Kentucky bluegrass: This grass requires led to the release of varieties of a number of copious amounts of water in summer if it is Australian native grasses that produce to retain a good appearance. excellent lawns in most of the urban areas of Perennial ryegrass: This is another heavy southern Australia even when they cannot be water user. watered. Although they are C3 grasses, they Chewings fescue: This will not compete are much better able to tolerate dry with other cool-season grasses unless soil conditions than are any of the imported pH is fairly low (about 5) and soil C3 grasses. phosphorus concentration is low. Bentgrasses: Shallow rooting means that Weeping grass (Microlaena stipoides): these grasses must be watered frequently Three varieties that are suitable for urban in dry weather. landscapes were available at the time of writing. Two of these, Griffin andNone of these grasses will produce a good Shannon, were developed through 20 yearslawn when water restrictions are severe. As of research at the University of Newthere are better alternatives, they should no England, Armidale, in New South Wales.longer be used for most Australian lawns. Griffin is fine and soft and produces an excellent lawn; Shannon is low growing and dense and is ideal for roadsides, verges and golf roughs. The third variety, Tasman, which was released in 2007, was developed from populations found in the King Lake district of Victoria by Native Seeds Pty Ltd. It may therefore be better suited to cold areas than are the other two varieties. Wallaby grass (Austrodanthonia species): When sown thickly, Hume Wallaby grassPlenty of water guzzlers here. (Austrodanthonia richardsonii var. Hume) 12 – LAWNS 119
  • 129. Table 24. Tolerance of cool-season grasses to various stresses, in order of drought tolerance Water Drought requirement for Salt Shade Frost Wear Grass tolerance good appearance tolerance tolerance tolerance tolerance Weeping grass excellent low medium excellent high good Wallaby grass excellent low good poor high fair Tall fescue medium very high medium good high very good Perennial ryegrass fair high poor medium high good Fescues (other) fair medium poor poor high good Kentucky bluegrass poor high poor fair high fair Bentgrasses poor high medium medium good poor produces a good lawn that needs virtually Redgrass (Bothriochloa macra): The turf no maintenance other than a couple of variety of this Australian native grass is mowings a year. It is ideal for shallow soils called Bass. It grows well in infertile clay and where the lawn cannot be watered. soils. Because it goes dormant in late Oxley (Austrodanthonia geniculata var. autumn, it is best to grow it mixed with Oxley) is slow-growing and highly Wallaby grass. The redgrass is green from persistent. It is suited to both parks and spring to autumn and the Wallaby grass is lawns. green during the cooler months. Once established, this combination will need noThese grasses establish slowly. It is essential irrigation even where annual rainfall isthat you sow seed thickly and undertake a only 400 mm.vigorous weed control program until full Couch and hybrids: Wintergreen, Santacover is achieved. Sowing a blend of these two Ana, Conquest, Windsor Green, Grandgrasses provides an excellent ground cover Prix and Greenlees Park have been widelywith low maintenance needs and very low used, with Wintergreen probably the mostwater requirements. If possible, use plugs popular. All give denser lawns than doesrather than seed to establish these grasses.Instant lawn of these grasses is going to beavailable in Victoria in early 2008.Warm-season grasses for southernAustraliaThe warm-season grasses use the C4photosynthesis system, so they are moreefficient at growing under water stressconditions than are cool-season grasses. Wintergreen.120 GOOD GARDENS WITH LESS WATER
  • 130. Table 25. Other information about cool-season grasses Fertiliser Preferred needs*; mowing annual height for Maximum Approximate grams of Preferred drought depth of root number of nitrogen per soil pH tolerance penetration mowings per square Phosphorus Grass range (cm) (m)^ year metre requirement Weeping grass 5–6.5 >5 1.2 6 once; 4 very low Wallaby grass 4.5–7.5 >5 1.5 6 once; 3 very low Tall fescue 5–8.5 5–7.5 1.1 30 monthly; 14 moderate Perennial ryegrass 5.5–8.5 2.5–5 0.5 25 monthly; 10 moderate Fescues (other) 4.5–6 2.5–6 0.4 20 monthly; 8 low Kentucky 6–7 3–7 0.4 30 monthly; 14 moderate bluegrass Bentgrasses 5.5–7 0.5–2 0.3 25 monthly; 12 moderate ^ Root penetration and total root mass decrease rapidly as mowing height is reduced. * Monthly to every six weeks during the season of active growth, unless otherwise stated. See the end of this chapter for information on how to provide these amounts of nitrogen and other nutrients. common (seeded) couch. The first two prefers sandy soil with excellent drainage. tend to stay green longer in winter than do Lower salinity water is needed during other cultivars. establishment. Buffalo: Common buffalo produces a Kikuyu: This grass is really tough and harsh-feeling lawn. There are now 10 drought-tolerant, but is so aggressive that it varieties that have a softer feel. Highly easily invades garden beds. Its rhizomes popular are Sir Walter and Palmetto. They can easily grow under lawn edgings and have the same water use efficiency as paths. It is too aggressive for many common buffalo. gardens. Seashore paspalum (Saltwater couch): Zoysia: Selections of two Zoysia species are Common names for it include Saltene and available for lawns. Their deep rooting Sunturf. Velvetene is an Australian variety habit makes them highly tolerant of that has excellent turf characteristics. It is drought, but they are slow to recuperate so good that it is a direct competitor to the from damage. Zoysia tenuifolia (Mascarene couches and the improved Buffalo grass) has the finest leaf, but is more frost varieties in areas from the latitude of sensitive than the others. Zoysia japonica Sydney–Adelaide–Perth and north. But it var. Empire and var. Empress are coarser, is particularly useful where soils and waters but more cold-tolerant. Zoysias are best are too salty for other grasses. No suited to warm to hot and humid climates reduction in the quality of established with minimal temperature fluctuation, but Velvetene is seen even when the irrigation they grow well as far south as Sydney. water has an EC of 24 dS/m (about half Siro Shadegro (Panicum laxum): This is a the saltiness of seawater). This grass low-growing tufted grass for sub-tropical and 12 – LAWNS 121
  • 131. Table 26. Tolerance of warm-season grasses# to various stresses, in order of drought tolerance Water Drought requirement for Salt Shade Frost Wear Grass tolerance good appearance tolerance tolerance tolerance tolerance Redgrass excellent low good excellent fair good Queensland blue excellent medium very good poor poor very good couch Zoysia excellent low medium good poor excellent Kikuyu excellent high medium poor poor excellent Couch and hybrids* excellent to low good poor fair good good, depending on variety Seashore paspalum good medium extreme good fair very good Buffalo good medium good excellent poor fair Siro Shadegro good medium low excellent fair excellent Broadleaf carpet grass poor high poor good poor poor # Within a species, different varieties often have different responses to various stresses. * See www.watercorporation.com.au/w/waterwise_index.cfm for information about the different varieties. tropical conditions, but it can grow south make firm recommendations for particular along the coast as far as Sydney. It grows well areas, but some general guidelines are: in heavy shade (down to 15–20% light). Only in Tasmania and at the higher elevations of the Blue Mountains, Southern Tablelands, the southern AlpsWarm-season grasses for the tropics and the Dandenong Ranges is it now Zoysia: See details above. possible to have an excellent lawn with Queensland blue couch: It is well suited to imported cool-season grasses. But even the Gold Coast–Brisbane–Sunshine Coast there, restrictions on water use make it region. much more sensible to choose one of the Broadleaf carpet grass: High water more highly drought-tolerant native requirements make it less suitable than cool-season grasses, especially Weeping zoysia under low-water conditions. grass. Dawson (Bothriochloa pertusa var. In other cool mainland areas, the choice is Dawson): Low-growing, dense turf for the between the native cool-season grasses and high rainfall tropics. one of the warm-season grasses. If your microclimate is frosty and cold during the winter, the native grasses will be your bestSummary for lawn grasses for southern choice. For less frosty and somewhatAustralia warmer areas, the native cool-seasonThe many different climatic niches found in grasses may be OK, but the warm-seasonsouthern Australia make it impossible to grasses are likely to give better results.122 GOOD GARDENS WITH LESS WATER
  • 132. Table 27. More information about warm-season grasses# Fertiliser frequency*; Preferred Approximate annual grams Preferred mowing height Maximum number of of nitrogen soil pH for drought depth of root mowings per per square Phosphorus Grass range tolerance (cm) penetration^ year metre requirement Redgrass <5.5 >3 1.8 4 once; 3 very low Queensland 5.5–6.5 1.5–3 1.5 25 monthly; 14 moderate blue couch Zoysia 5.5–6.5 3-5 1.0 2 twice; 5 moderate Kikuyu 6–8 2–4 2.4 25 monthly; 14 moderate Couch 5.5–8 1.5–3 2.4 20 monthly; 14 moderate Saltwater 6–8.5 2-4 1.5 15 several; 5 moderate paspalum Buffalo 6.5–8 5–7.5 1.0 20 monthly; 12 moderate Siro Shadegro 5.5–6.5 3.5 1.0 4 once; 3 low Broadleaf 5–6 1.5–3 0.3 20 monthly; 8 moderate carpet grass # Within species, different varieties can have different requirements. ^ Root penetration and total root mass decrease rapidly as mowing height is reduced. * Monthly to every six weeks during the season of active growth, unless otherwise stated. See the end of this chapter for information on how to provide these amounts of nitrogen and other nutrients. The warm-season grasses will be dormant For a lawn for a new house, you must and pale in winter and the native cool- prepare the subsoil of the area as season grasses may be a bit pale under described on p. 107. Have the top of the severe summer drought conditions. subsoil at such a height in relation to Mixtures of appropriate warm and cool- paths, etc. that you allow for the depth of season grasses will give the longest green topsoil that you want. Topsoil depth time. should be at least 200 mm. For warmer–hotter–drier areas, only The topsoil should be of sandy loam warm-season grasses should be used. texture for warm-season grasses, but it should have more clay (up to 20%) if you are growing native grasses.How to succeed with new and If the lawn is to cope with heavy use forrenovated lawns games, the topsoil must have anPrepare the soil properly infiltration rate of at least 50 mm/hr (see p. 108). This may sound high, but it willIt is essential that the roots of your chosengrass are able to penetrate deeply into the decrease as roots clog soil pores andsoil. This deep penetration allows them to use people run and jump on the grass.the greatest proportion of the rain that has Include fine compost in the top 100 mm ofsoaked into the soil. the topsoil, but not below that. Compost 12 – LAWNS 123
  • 133. Remaking a lawn Those whose lawn has thinned or died because of water restrictions, but who would still like to have a lawn, can remake the area with one of the native grasses or warm-season grasses listed above. First, scrape away the old turf and any thatch that has developed on the soil surface. This valuable, but probably weedy,Screening finished compost at Jeffries, SA. material can be composted and used on garden beds. included in deeper soil can become Check the infiltration rate of the anaerobic and kill the grass. remaining soil (see p. 108). Relieve any If you intend to grow a native grass or compaction, as described on p. 107. zoysia, it is essential that the topsoil have a Check the pH of the soil and take low concentration of available phosphorus. corrective action as needed. This will favour the growth of the slower- Check for any layers and take remedial establishing natives and zoysia over weeds. action, if necessary. The topsoil is to be spread and firmed Form the existing soil to the final down, not compacted, and its surface contours. formed to the final contour of the lawn. If needed, top up with soil of sandy loam If you are using a poultry manure-based texture. fertiliser, now is the time to apply it. Incorporate fertilisers if a need has been Spread at the recommended rate and rake shown by laboratory testing. it into the soil. Keep applications of Sow seed or lay the new turf. Instant turf poultry manure products to one-third of of weeping grass and combined weeping the recommended rate when you are going grass, wallaby and redgrass turf should be to grow native grasses or zoysia. available in Victoria by the time this book If you are going to install dripper lines, goes to press (check on the internet). now is the time to do it. These should be run at 10–15 cm below the surface. They When to sow or plant need to be no further apart than 15 cm in The best time of year for sowing/planting a a sandy loam, and 20 cm in less sandy soils. lawn depends on your climate and on the Use only the special dripper line that is type of grass to be used. A main aim is to take suitable for burying in soil. maximum advantage of rain during The top of the topsoil should be the establishment. final height if the lawn is to be established from seed, but a little lower if turf is to Cool-season grass seed should be sown in be used. either mid-autumn or early spring. Winter124 GOOD GARDENS WITH LESS WATER
  • 134. sowings take too long to germinate. No Start laying the turf along a straight edge further information is given, because most of the area. Roll out the strip and pull it lawns are now established with turf hard up against the edge. (‘instant lawn’). Lightly tamp the turf with a broad, Cool-season grass turf can be laid out flat tool made from thick boards and from mid-autumn to early spring, the a pole. earlier the better. Any hollows should be filled by spreading Warm-season grass turf has traditionally more soil under the turf; any humps been laid out from early spring to early should be removed from underneath the summer in the south and throughout turf. the wet season in the north. Trials in Stand on a wide plank placed on the first Melbourne have shown that early autumn strip when laying the next strip. turfing, when the soil is still warm, can Stagger joints in the same way as when be successful. As average temperature bricks are being laid. climbs, autumn turfing will become Do not have short pieces of turf at the ends more viable, so long as water for of rows of turf. Rather, have full pieces at establishment is available. Laying in high each end of a row and any short piece summer is not sensible in the south unless needed towards the middle. you can apply plenty of water during Trim the turf with a sharp kitchen knife establishment. when it has to be fitted around curves or cut to fill a gap. Water the turf within an hour of laying inLaying strips or squares of turf (‘instant warm weather, sooner in hot.lawn’) Water the soil a day or two before laying the turf. Have the turf delivered no more than one day before it is to be laid. Keep the exposed surfaces of the turf moist by frequent light sprinkling. Do not cover them with plastic sheeting. The soil surface must be lower than the surrounds of the area by the thickness of the turf. Spread a light dressing of lawn fertiliser over the levelled soil and rake it into the soil. Lay turf strips up and down sloping ground. Start at the bottom of the slope. Frequent watering in the first week after laying will Peg it in place on steep slopes. prevent this. 12 – LAWNS 125
  • 135. Water daily to several times each day for Once you have full cover, give the soil a the first two weeks in warm to hot weather, thorough and deep soaking if rain has not less frequently in cool. done this for you. Your aim is to make sure that the subsoil is moist. Then increase the time between waterings,Early care of new lawns so as to encourage the roots to grow deeply For all grasses EXCEPT native grasses and into the soil. zoysia, apply lawn fertiliser with an NPK All this effort will be wasted if you do not composition of something like 10-2-6 at a regularly wander over your lawn and rate of about 20 g per square metre (g/m2) remove or selectively spray weeds while each two weeks to seedling lawns until they are young. Letting them go to seed or coverage is complete. Then reduce the allowing such nasties as creeping oxalis to frequency to monthly or every six weeks. spread unchecked will soon give you a One early application may be all that weed patch. A few minutes each couple of instant turf needs before you start the weeks will keep your lawn looking regular program. attractive. Seedlings that do not respond to the first couple of fertiliser applications, and look dull green to yellow with purple colours, Watering lawns are probably suffering from phosphorus Much more information about watering is deficiency, due to there being little in the given in Chapters 7 and 8. Here are just a few sandy soil blend you have used. When important points for lawns. this happens, switch to a general garden If a ban on the use of sprinklers means fertiliser with a composition of something that your established lawn can only be like 10-4-6 until the grass greens up and watered by hand, it may be better not to starts to grow. An alternative is to apply water it at all. Let it go brown. If rain is not single superphosphate at a rate of 25 g/ too many months in coming, the warm- m2 and continue with the 10-2-6. Reduce season grasses and native grasses will shut the frequency once you have full cover. down, but not die. Prolonged drought will If native grasses or zoysia look pale and are thin out or kill imported cool-season not growing well, apply a mixture of urea grasses, so giving you an opportunity to and potassium sulphate (1:1) at 5 g/m2. It grow something tougher. is particularly important that you do not In southern Australia, if you are able to apply phosphorus to native grasses. Doing divert water from a rainwater tank or the so will just encourage weeds to out- laundry, you should be able to keep a lawn compete them. of grasses suited to the area going with Mow as soon as is possible – probably perhaps two deep soaks (each of about one month after sowing seed and 50–100 mm) during summer. one week after laying turf. Mowing will Where watering is possible, it must be encourage the grass to thicken up. infrequent and deep. That generally126 GOOD GARDENS WITH LESS WATER
  • 136. means no more often than once a month. cut the grass as high as possible. This might This encourages deep root penetration sound upsidedown, but think of it this way: and maximum drought tolerance. It also root growth depends on photosynthesis in discourages the growth of shallow-rooted leaves. Tall-cut grass has a much larger leaf weeds. area than does grass cut as short as bowling green grass, so it is able to support a much deeper root system. It will of course transpireMowing more water than will shorter grass, but this isA fundamental rule for lawns is that the grass more than compensated for by its ability tomust be mown frequently enough so that you remove water from a larger volume of soil.never remove more than one-third of the This applies particularly to cool-seasongreen leaf area at any one mowing. That grasses. The more horizontal growth habit ofcould mean twice each week at the peak of the lawn types of warm-season grasses such asthe growing season to less than monthly when couch means that this effect is smaller withthere is little growth. The sudden removal of them. When cut relatively short they can stillleaves caused by mowing inevitably reduces have a deep root system. Follow the guidelinesroot growth for a while. A cycle of rank in Tables 25 and 27.growth and scalped grass caused byinfrequent mowing will severely damage For cool-season grasses, keep mowingroots. The weakened plants with their shallow height moderately high during spring,roots have a poor ability to withstand drought raise it during summer and graduallyor other stress. Soon all you will have is a lower it during autumn. For warm-seasonweed patch. grasses, mowing height can be high duringAnother fundamental rule is that to spring, gradually lowered during summermaximise depth of rooting, and hence and then raised again during autumn tomaximise the grass’s access to water, you must promote winter hardiness. If you don’t like mowing, and you have difficulty finding the cash for a contractor to do it as frequently as is desirable, you need to look at Tables 25 and 27. There, you will see listed a number of grasses that need far fewer mowings than do many of the grasses that are commonly grown. Choose one of them for a new lawn or use them when you remake your existing lawn. Until the cut ends of leaves left by mowing seal over, they lose water at a faster rate than does the rest of the leaf. This loss is greater through ragged cuts left by bluntScalping: on the road to a weed patch. mower blades than through the clean cuts 12 – LAWNS 127
  • 137. from sharp blades. By regularly Compaction sharpening mower blades, you make a Clay soils under lawns can be severely further small contribution to the well- compacted by heavy use for games or general being of your lawn. traffic. The resulting poor drainage can Don’t mow on days when the temperature seriously reduce root growth and lead to a is likely to exceed 35oC. rapid decline in lawn quality. The compaction Don’t mow immediately after watering or may be temporarily relieved through coring. substantial rain. Doing so may compact the Remove the core material and fill the holes soil. with sandy loam. Long-term care of heavily used lawns is easiest if the uppermost 200 mmDealing with thatch of the soil is a sandy loam.Thatch is a layer of dead and living shoots,stems and roots that develops on the surface Fertilising lawnsof the soil below the leaves of lawn grasses. A Water use is minimised if you apply only thethin layer of thatch is desirable because it amount of fertiliser needed to keep the lawngives spring to a lawn and cushions the soil just growing. The grass is then at its mostagainst compaction. A thick layer is efficient at extracting water from the soil,undesirable because it can reduce water but is not losing excessive amounts by havingpenetration into the soil, increase disease a huge amount of leaf. Excessive use ofproblems and allow scalping of the grass. It fertiliser nitrogen produces heavy leafoften becomes water repellent. The grass will growth and a marked decrease in rootthen not get the full benefit of rain as some of growth. So not only does heavy fertiliser usethe rain will either run off the lawn before it increase water use (and thatch productioncan soak through the thatch, or it will soak in and mowing frequency), it also reduces theunevenly and give the lawn a patchy ability of the grass to reach water in the soil.appearance. Water repellence is overcome by Water a lawn thoroughly before applyingapplying a wetting agent. To minimise thatch soluble solid fertilisers. Allow the leaves todevelopment, do not apply more fertiliserthan is given below.Thatch decomposes naturally when moist andnot too acidic. A common cause of slowdecomposition is that the thatch has becometoo acidic from fertiliser applications. Checkthe pH of the thatch layer in your lawn. If it isbelow 6, applying lime at a rate of 0.5 to 1 kg/m2 will speed up decomposition. Applyingsugar (about 50 g/m2) with the wetting agentand lime will further speed thatchdecomposition. A mulching mower.128 GOOD GARDENS WITH LESS WATER
  • 138. dry off, apply the fertiliser and then WATERAGAIN IMMEDIATELY TO PREVENTLEAF BURN.Do not fertilise grass that you cannot water orwhich is dormant.Here are two strategies for fertilising lawns: This lawn fertiliser contains methylene ureas – a slow-release source of nitrogen. It is an alternative to the ‘easiest’ fertilising method when some extra phosphorus is also needed.Lawn fertilising at its easiest Use a mulching mower so that losses of Note that the rate recommended here may nutrients from the lawn are minimal. be lower than that recommended on the For soils that are amply supplied with bag. There is little point in adding large phosphorus, annually, at the start of the amounts of fertiliser that will give large growing season, for all grasses except the amounts of growth that will have to be native grasses and zoysia, apply a removed by mowing. synthetic slow-release source of nitrogen Continue to apply the fertiliser at a low (Blue Chip or IBDU) at a rate of 30–40 g rate every four to six weeks of growing per square metre; apply potassium season. Change the rate and/or amount sulphate at 15 g per square metre once a depending on grass response. year just before the season of slowest grass Towards the middle of autumn in southern growth. Australia, replace half of your application For native grasses, the application rates are with an equal weight of potassium no more than one-third of the above and sulphate. The extra potassium will for zoysia and Seashore paspalum about toughen up the grass. half.Lawn fertilising with much more effort Buy a fertiliser specially formulated for lawns. The fertiliser will have an NPK content of something like 10-2-6. Apply the fertiliser at a low rate at the beginning of the main growing season, but not when it is too cold for the grass to grow. A typical rate is 20 g/m2. Half this rate could give satisfactory results if clippings are not removed. … and no evaporative cooling. 12 – LAWNS 129
  • 139. Earthenware ‘pots’ in the desert.
  • 140. WAT ER F O R PL A N T S I N P OT S KEY POINTS Basics of potting mixes Balance between air and water in potting mixes Over-watering and its prevention Using additives to extend the time between waterings Wetting agents and their use How often to water Providing water via hoses, drippers and by sub-irrigationA plant in garden soil can send its roots in all with a small amount of sand, but no naturaldirections to the limits of its genetic soil. The main organic material used iscapabilities. When it tries to do that in a pot, composted pine bark, but there can beits roots soon hit an impenetrable barrier. varying amounts of composted sawdust,The amount of water available to a plant in a composted green organics, coir fibre dust,container is therefore strictly limited to natural peat, animal manures and so on.something less than the volume of thecontainer. You have to repeatedly top up thatvolume if you want the plant to remain alive.If you find this a hassle, it is easy to automatethe watering.A first requirement is that you understand alittle about the basics of potting mixes andtheir properties.Potting mixesAll potting mixes sold in Australia are nowmixtures of organic materials, sometimes Grafted darwinias in full flower. 131
  • 141. Australian Standard mixes carry the StandardMark on their bags. It is recommended that you buy only those potting mixes whose packs carry this StandardMark. This Mark guarantees that the mix in the pack has been produced with properties that conform to the Australian Standard for Potting Mixes. That guarantee is backed by independent checking of the quality control records at the factory and of independent analysis of random samples. Feedback from the analyses ensures that quality is maintained from batch to batch.Scaevola aemula makes an attractive addition to anypatio. (Photo: Rodger Elliot)Humus produced by the decomposition of What the Standard does not coverthese organic materials takes the place of the The Standard does not cover anything thatclay of soils. Cheaper mixes tend to have you do to the mix before you use it, nor doeshigher proportions of sawdust and other it compensate for poor growth that is due towood wastes. Quality varies considerably. The poor environmental conditions around abest potting mixes conform to one of the two potted plant. Keep in mind that:grades of the Australian Standard for Potting All plants in all potting mixes eventuallyMixes (see box). need more fertiliser than is in the potting mix when you buy it. Over some months in pots or in the bag, even mixes that were manufactured according to the Standard may become more difficult to rewet if they get dry, no matter how excellent rewetting was when you bought the mix. That is a natural effect of continuing activity by microbes living in the mix. You will then need to improve wettability by adding a wetting agent. Soluble nitrogen in Premium mixes will be steadily used by microbes so, after a couple of months of storage, you will still need toA potted agave would look good in any courtyard. add fertiliser at potting.132 GOOD GARDENS WITH LESS WATER
  • 142. AUSTR ALIAN STANDARD P OT TING MIXESAustralian Standard AS 3743–2003 (and updates) worth this extra cost. After all, the cost of therequires that a potting mix that is claimed to potting mix is usually small compared with theconform with it must have physical and chemical cost of the plant you put in it.properties that ensure good plant growth. All Standard Regular mixes are not required to havemixes must: soluble nitrogen in them when sold. It is essential drain well; a minimum air-filled porosity of with them that you use a fertiliser at potting. 13% (see later in this chapter) is specified for Either include a controlled-release fertiliser in the general-purpose mixes mix before potting or start a soluble fertiliser be easy to rewet should they dry out in the first program immediately after potting. You will couple of months of use usually find that you will use less fertiliser with contain all trace elements in amounts that will these Regular mixes than you need to use with be adequate for plants for one year non-Standard mixes. contain adequate initial amounts of the The cheapest way of ensuring that your plants get nutrients potassium, calcium, magnesium what they need is to use a Standard Regular mix and sulphur that are in balance with one that has the right air-filled porosity for your plants another and, just before potting, add a combination of contain a level of phosphorus that is suited to slow-release fertiliser (e.g. Nitrophoska Slow the plants to be grown. Mixes for phosphorus- Release) (1 g/L) and controlled-release fertiliser sensitive plants have lower concentrations of (3–6 g/L), plus wetting agent. phosphorus than do general-purpose mixes have a suitable pH. General-purpose mixes must have a pH in the range 5.3–6.5; the pH PREMIUM REGULAR of mixes for acid-loving plants is to be in the range 4.8–5.8.Standard Premium mixes must also have a supplyof nitrogen sufficient to give at least one month ofgood plant growth even when other fertiliser is notused. In other words, you can transplant a smallplant into newly bought Premium mix straight fromthe bag and expect the plant to grow well for atleast a month before you need to apply fertiliser.The costs of testing and maintaining the high Australian Australianquality of these genuinely Premium mixes means Standard Standardthat they cost more than do other mixes. You will AS3743 Lic No 961 AS3743 Lic No 961usually find the response in your plants is well Standards Australia Standards Australia 13 – WATER FOR PLANTS IN POTS 133
  • 143. Non-Standard mixesYou take pot luck with potting mixes thatmake no claim for compliance with theAustralian Standard. Some mixes may Solidsproduce satisfactory results, but spot checking 30%has shown that they vary enormously in Waterquality. It is impossible to tell whether the 50%contents of a particular bag will or will notgive good growth, even with the best of Airfertilisers. Any manufacturers who claim to 20%have excellent products will long ago havebacked these claims by testing, and will beproducing according to the Standard. Approximate proportions of solids, water and air in a general-purpose potting mix.Potting mix properties produce a product that has the same range ofA quick sketch of the main properties of particle sizes.potting mixes will give you a solid basis for Particle size range determines how the mixunderstanding how to manage your plants in behaves towards water and air.them. Think of two pots, one filled with fine beach sand, the other with coarse gravel.Air and water Obviously, the spaces (pores) betweenA potting mix is composed of particles of particles in the sand are much smallervarious sizes. These particles provide the than those in the gravel. The gravel isstructure of a potting mix in the same way more ‘open’ than the sand.that aggregates and sand grains give soils Now think of watering the two pots. Aftertheir structure. Potting mix producers screen drainage has stopped, the sand will beraw materials such as pine bark to various saturated almost to the top of the pot. Inparticle size grades and then re-combine fact, knocking the pot will probably causethese grades so as to give each product the a slurry of sand to run from the drainagerequired structure. For example, a mixture holes. Few pores, if any, contain air. On thefor germinating seed needs to be quite fine, other hand, the only water held by theso only particles smaller than about 5 mm are gravel will be a film on the surfaces of theused. A potting mix for general use will be particles and in the narrowest parts ofcoarser, with particles up to perhaps 12 mm pores where particles touch. The rest ofacross. Orchid bark typically has all particles the pores contain air.larger than about 10 mm. The skill required The sand will contain too little oxygen forby a potting mix producer is to consistently the roots of most plants; the gravel will not134 GOOD GARDENS WITH LESS WATER
  • 144. Table 28. Desirable air-filled porosity of potting mixes for different situations, as measured by the Standard Method Desirable air-filled porosity Approximate water-holding capacity Situation (% volume) (% volume) Seedling native plants in tubes 9–12 (least open) 60+ Seed-raising mix for punnets 10–15 60+ Mix for larger outdoor pots 10–15 50–60 Ferns 12–18 50–60 General indoor plants 15–25 45–60 Propagation mix 20–25 30–40 Cymbidium orchids 20–30 30–50 Epiphytic orchids 35–50 (most open) <25 hold enough water for any plants other Effect of pot depth on air-filled porosity than epiphytic plants such as tropical Potting mix in a pot behaves in much the orchids. same way as a saturated towel on a clothes line. Just after drainage has stopped, thePotting mixes must have a better balance of bottom part of the towel is still saturated withair and water than this. Manufacturers give water. Above the saturated part is a very wetthem this balance by carefully adjusting the zone, with water content then grading to theproportions of particles of different sizes. Two lowest level at the top of the towel. A bathterms are used to describe this balance towel and a hand towel of the same thicknessbetween air and water. One is ‘air-filled hanging side by side on the clothes line willporosity’ (AFP), which is the percentage of each be seen to have the same depth ofthe volume of a potting mix in a container saturated and very wet zone. But the shorterthat is air space when it has just finished height of the hand towel will mean that itsdraining following watering. In other words, average wetness will be greater than that ofit is the minimum percentage of air that will the bath towel.be in the mix. Evaporation and transpirationsteadily remove water from the mix and sosteadily increase the proportion of the mix Effect of container height on AFPthat is air. The other term is ‘water-holding Air-filled porosity (%)capacity’. It is the proportion of the mix thatis water when drainage has just stopped. It is arather crude measure, because not all of thiswater is available to plants. But knowing thewater-holding capacity of mixes is useful forcomparing them (see Chapter 14 for simplemethods that you can use to determine the Height of container (cm)AFP and water-holding capacity of a potting As pot height increases, the proportion of air in a mixmix). increases. 13 – WATER FOR PLANTS IN POTS 135
  • 145. So it is with potting mix in pots. The depth of The way to prevent over-watering even whensaturated and very wet mix is the same no you water frequently, is to use a potting mixmatter what the total height of the mix. For that has an air-filled porosity in the range 18the one mix, the average wetness is greater to 25%. Roots in a mix of this openness willwhen it is in a shallow pot than when it is in a rarely suffer from lack of oxygen. Thetall pot. Conversely, the proportion of air in a downside of such a mix is that it holds lessjust-drained mix will be less when it is in a water than a tighter mix, so you will need toshallow pot than when the same mix is in a water more frequently.tall pot. A potting mix in which the balance You have a choice:between air and water is good in a shallowseedling punnet may contain so little water in Use a mix with low air-filled porosity anda tall pot that frequent watering of plants will be very careful about how often you applybe necessary. On the other hand, a mix that more water, or,has excellent properties in a tall pot will Use a more open mix, water as frequentlyprobably contain too little air when placed in as you like and forget about creatinga squat pot. problems for your plants from over- watering.Changing the width of a container or the Here are some guidelines for choosinggeneral shape of its sides has no effect on the potting mixes:proportions of air and water in potting mixin it. Of course as pot size increases, the For shallow containers – squat pots –total amount of water available to a plant in choose a mix with an air-filled porosity atit increases. the upper end of the 20–25% range. This does not apply to bonsai. For plastic and glazed ceramic containers of 1 L to about 5 L capacity, choose a mixBalance between oxygen and water with an air-filled porosity at the lower endThe Australian Standard for Potting Mixes of the 20–25% range. For similar pots withrequires that conforming mixes have an air- capacities up to about 10 L, choose a mixfilled porosity of at least 13%. This is really with an air-filled porosity in the 15–20%an absolute minimum. A mix with this or range.lower air-filled porosity will have a high For tubs and deep (deeper than aboutability to hold water, but there is a danger 30 cm) planter boxes, the potting mix canthat, with frequent watering, roots in the have an air-filled porosity of around 10%.bottom of the container will be constantly It can contain fine sand or even 20–30%wet and will become stressed through lack of loamy soil.oxygen. Stressed roots are easily attacked by Hanging baskets lined with naturalany pathogens in the mix. They rot and soon coconut fibre or a porous syntheticthe whole plant is dead. Gardening books material and unglazed ceramic pots loserefer to this as ‘over-watering’. water through their sides. This evaporation136 GOOD GARDENS WITH LESS WATER
  • 146. is useful, even essential, for plant survival about one-third by volume is a useful during summer as it cools the plant’s roots. starting point. But of course the potting mix does dry out The coarse material that is easiest to faster than if it were in plastic pots of obtain is usually orchid mix. Other coarse similar volume. This more rapid drying materials include very coarse sharp sand, allows you to use a fairly tight mix in them, 3 mm gravel (including scoria, but say with an air-filled porosity of around absolutely not crushed limestone or 15% where evaporation rates are fairly marble, because they can raise mix pH high. If you use a more open mix your high enough to cause trace element plants may suffer from frequent deficiencies) and coarse bark. dehydration. You can reduce air-filled porosity by Some books recommend painting the adding coir fibre dust (Cocopeat, etc.) or insides of unglazed ceramic pots to stop fine sand. Start with a 10% (by volume) evaporation through their sides. This is addition and check air-filled porosity silly. It is more sensible to choose a potting before adding more. mix that allows you to use evaporation to If your main aim is to increase water- aid plant survival in summer. holding capacity, coir fibre dust is the best material to use. Add 10 to 20% by volume. When you are able to modify a mix as youChanging the air-filled porosity of a mix wish, you can make it as open or ‘tight’ as you want. The choice is yours!Unfortunately, the bags in which pottingmixes are sold do not state the air-filledporosity range of the contents. If it is aStandard mix, you know that its air-filledporosity will be at least 13%, but that is all.Really all you can do is to buy a few differentbrands, check the air-filled porosity yourself(see Chapter 14) and then stick with the onethat best suits your conditions. Once you havetaken a few mixes through the test, you willget to know the feel of mixes of differentporosities and so more quickly choose on thebasis of initial feel. If you still can’t find asuitable mix, you can modify one as follows: To increase the air-filled porosity of a mix you must add something coarser to it. The amount needed depends on the fineness of the original mix and the degree of change needed. Often the addition of Composted pine bark of different gradings. 13 – WATER FOR PLANTS IN POTS 137
  • 147. WATER CRYSTAL S AND P OT TING MIXES While the various water crystals can hold up to crystals and surrounding particles as the mix dries 300 times their weight of distilled water (see means that there is limited transmission of water p. 52), when they are included in potting mixes, from them to distant roots. This effect will be the actual amount held is much less. This is greatest immediately after potting a plant and will because of the effect of fertiliser salts, physical decrease as its roots grow around and through constraints on expansion of the crystals in the mix the wet crystals. But even then, not all of the and their slow rate of water absorption compared water in crystals can be extracted by plants with the time taken to apply water. These effects before they wilt. mean that even the best water crystals hold only All this means that in contrast to the benefits seen about 20–40 g water per dry gram when incorpo- in sandy soils (see p. 53), the benefits of water rated into potting mixes (Table 29). crystals in potting mixes are rather smaller than In addition, not all of the water in the crystals can can be obtained by including 10–20% coir fibre be used by plants. Incomplete contact between dust in the mix. Table 29. Effect of four brands of water crystals on extra water held by a potting mix when they were added at a rate of 1 g dry/L mix Potting mix of 16% AFP Potting mix of 33% AFP Treatment Extra water held by Time to wilting Extra water held by Time to wilting mix (g/L) (hours) mix (g/L) (hours) Control – 61 – 55 Water crystal 1 6 59 20 60* Water crystal 2 7 61 34 60* Water crystal 3 14 60 35 62* Water crystal 4 24 64* 29 61* * Significantly different from time-to-wilting of control plants.Dealing with non-wetting mixes Difficulty in wetting is caused by the presenceOrganic potting mixes are often difficult to of waxy materials produced by fungi on therewet if they dry out either before potting or surfaces of particles. Dry mix can be rewet bywhen in pots. Suspect that the mix in a pot dunking the pot into a bucket of water for 10has become non-wetting if water pours minutes each time it dries out. This is ofrapidly out of the drainage holes at the start course a bit difficult with 30 litre tubs.of watering. The water has run down the Fortunately, there is an alternative to dunking.outside of the root ball or through the largerchannels in the mix and has hardly made itany wetter than before watering. Scratch Wetting agentsbelow the surface of the mix after watering. The simplest way of ensuring quick rewettingDryness indicates a non-wetting problem. of potting mixes is through the use of wetting138 GOOD GARDENS WITH LESS WATER
  • 148. 2. A granular solid, usually a calcined clay or coir fibre dust. These products are just mixtures of the liquid wetting agent with the solids. They generally contain 10 to 15% of the liquid wetting agent. Granular wetting agents can be more convenient to use than the liquids. Bentonite clay is also sold as a wetting agent. While it may be beneficial in sandy soils, research has shown that it does not overcome water repellency when added to potting mixes.Most of a water-repellent potting mix is not made wetduring normal watering.agents. A wetting agent is really just a special Ways of adding wetting agents to mix intype of detergent that is only slowly broken containersdown by microbes. The wetting agent allowswater to spread more easily across the Method 1surfaces of particles in the potting mix. When 1. Make up a solution of the wetting agentapplied at the recommended rate, the best by adding 1 mL of liquid concentrate toremain effective for four to five months. each litre of water. 2. Dunk each pot into the solution untilA common question is: ‘Why can’t I use cheap bubbling has stopped, indicating that thedishwashing liquid rather than those expensive whole of the potting mix is wet.wetting agents?’ The answer is that you can use 3. Remove and allow the excess to draina dishwashing liquid if you have nothing back into the dunking solution.better. Add 2–4 mL to each litre of water usedfor dunking or pouring onto the dry pots. Butyou also need to know that the effect ofdishwashing detergents disappears within aweek of addition, because the detergents indishwashing liquids are required by law to bebiodegradable: they are designed to bebroken down in less than a week by microbesin sewage treatment plants.Wetting agents come in two forms:1. A thick liquid. This has to be diluted with water before it is added to a potting mix. Applying a wetting agent solution. 13 – WATER FOR PLANTS IN POTS 139
  • 149. Method 2 Thus, a blast of warm, dry air from an air1. Make up a solution of wetting agent by conditioner in winter will cause plants to lose adding 1.5 mL concentrate to each litre water rapidly. A plant in a cool bathroom will have a very low rate of water loss. of water.2. With a watering can, slowly pour the Table 30. Rate of evaporation of water indoors, as affected solution all over the surface of the mix by air temperature, air humidity and rate of air movement. The figures are mm of water evaporating per 24 hours from until there is some drainage from the pot. a dish of water One metre in front of a typical airMethod 3 Relative Almost still air; conditioner; mm humidity mm water lost water lost1. Sprinkle granular wetting agent onto the of the air 18ºC 26ºC 18ºC 26ºC surface of the mix, at the recommended 90% (very 1 2 3 5 rate. humid) 50% 5 10 18 332. Water lightly to allow release of the 10% (very 10 19 22 48 wetting agent from the granules. dry)3. Water a little more heavily next day to flush the wetting agent into the mix. Other factors affecting rate of water loss are:Note: All wetting agents available in Australia Plant size: the larger the plant, the morewill not harm plants if they are used at the rapid the loss of water.recommended rate. But several of them have Pot size: for a given size of plant, wateringbeen found to reduce plant growth when they frequency can decrease as pot sizeare applied at two or more times the increases.recommended rate. Do not go above the Type of plant: many thin-leaved plantsrecommended strength or rate and do not from tropical lowlands seem unable to slowapply them more frequently than once every their rate of water loss as the growingthree months. medium dries out; they lose water until they are totally wilted. Plants with variegated leaves lose water more slowly than all-green plants of the same size.Matching watering with mix, plant andenvironmentTable 30 gives an idea of the effects of indoor Crockingenvironment on losses of water from potted Crocking is the practice of placing a layer ofplants. The main point to be gleaned from gravel or broken ceramic pots in the bottomsthe table is that decreasing humidity, of pots ‘to improve drainage’. As crockscombined with increasing draughtiness and reduce the height of the potting mix, theyair temperature, dramatically increases losses increase the average wetness of the mix aboveof water from pots. it. Crocking therefore increases the risk of140 GOOD GARDENS WITH LESS WATER
  • 150. damaging plants by over-watering. You can quickly check small pots by liftingCommercial nurseries worldwide annually them.produce hundreds of millions of potted Look at the surface of the mix in the pot.plants without crocking. Using a potting mix There is no need to water if it is obviouslywith a suitably high air-filled porosity is your moist.best guarantee of not harming pot plants by Investigate further if the mix looks dry orover-watering. is only slightly moist. Dig down a couple of centimetres. Dry mix indicates a need toOne place where crocking is useful is in the water. Moist mix probably means that youbottoms of pots without holes. The main such can wait another day.pots are terrariums. The spaces in the gravel Another check for large pots is to tap theact as a reservoir for any water added in side of the pot. A hollow sound probablyexcess of the holding ability of the mix. If the indicates a need to water.gravel were not there, the extra water would Feel the mix at a drainage hole. If it’s wet,be retained in the mix, making it too wet. don’t water.Crocking may also be desirable in terracottapots that have one relatively small drainagehole which is easily blocked. For hanging baskets Wire baskets that are lined with coconut fibre, bark or synthetic materials should beReducing evaporation from the mix watered if the bottom of the basket feels dry.You can increase the time between waterings Test plastic hanging pots as given above forby mulching the surface of the mix. Use any pots.coarse, decorative material such as barknuggets, water-worn pebbles, coloured wood Less satisfactory methodschips, scoria or gravel (not marble or Daily watering may be satisfactory inlimestone, because they will raise mix pH summer for outdoor plants in open mixes,high enough to cause trace element but in cool weather and for plants in lessdeficiencies). The depth need be no more open mixes, a constantly wet mix can leadthan one or two particle thicknesses. A less to rotting of roots.decorative alternative is to place a disc of coir Moisture probes are inaccurate and can bematting on the surface of the mix. very misleading. They usually still read ‘wet’ when the mix is too dry for good growth of plants. The amount of fertiliserDeciding when to water plants in in the mix affects the reading.containers Never water a wilted plant if the mix is still wet. The wilting probably means that theFor pots large and small plant’s roots have been damaged. A droopy plant is telling you what you Withholding water may enable the plant to should have done some time ago. recover. 13 – WATER FOR PLANTS IN POTS 141
  • 151. Amount of water to apply Don’t ever just sprinkle a bit of water onto the surface of the mix. Rather, add enough water so that a little runs out the drainage holes. If your water is saline, add enough so that an amount equal to about 10% of pot volume runs out the bottom. Excessive drainage causes excessive loss of nutrients. The drainage water which is caught in a saucer under pots indoors can be left there for later use by the plant. If the potting mix is open enough, the water in the saucer will not harm plant roots. Knowing the temperature of potting mix in a pot can The more salty your water, the more be very informative. frequently you must flush the pot to remove excess salts. Frequency of flushing Sun shining directly onto the outsides of can range from monthly to annual. pots will heat the mix inside. Even on a mild day (22oC) the temperature on the sunny side of black plastic pots can exceedTemperature in pots 40oC; on a hot day, the temperature canThe natural situation for most plants is for quickly exceed 50oC. Temperatures risetheir roots to be in an environment of more highest in dark pots on light backgrounds,even temperature – and during the day, lower so where summers are hot, prefer light-temperature – than that around their tops. coloured pots. Always shade plastic pots onThe situation can be quite different in pots. warm-to-hot days. As root temperature increases, both In the shade, the temperature of the outer evaporation of water from the mix and part of mix in a plastic pot will be about transpiration from plants increase rapidly. the same as that of the surrounding air. Watering must be more frequent. Up to an air temperature of about 30oC, Evaporation of water from the sides of the roots of most plants likely to be grown wire hanging baskets and unglazed in pots will not be harmed. In fact, terracotta pots will cool the mix inside by temperatures in the 20s give maximum several degrees. This cannot happen growth rates for many plants. through the sides of plastic or glazed (or But as mix temperature goes into the 30s, painted) ceramic pots. Plants tend to roots will be increasingly stressed. The survive best in hot weather in baskets and roots of many plants are killed by several unglazed pots – as long as you water often hours of temperatures over 40oC in the enough to make up for the more rapid loss of mix. water from them.142 GOOD GARDENS WITH LESS WATER
  • 152. Therefore, if you live in an area where You get to enjoy your plants as you water summer temperatures often exceed 35oC, them. ignore any advice to seal the inside You notice problems such as attack by surfaces of unglazed ceramic pots. caterpillars or aphids, so you can take Many indoor plants, being from the corrective action before there is much tropics, do not like low temperatures. damage. Daytime temperatures should be at least Each plant can be given exactly what it 15°C. Night temperatures as low as 5°C are needs. tolerated by some species but not others. See the end of Chapter 8 for information Sudden changes in temperature should be about using drippers to water plants in pots. avoided: in winter, warm irrigation water to about 20°C. Tropical plants being grown in cool areas will have warmer roots if they are grown in Sub-irrigation plastic pots rather than in terracotta pots. Sub-irrigation is a general term used for systems that deliver water to plants via the bottom of the container. For successful use ofWays of watering plants in containers sub-irrigation you must:Water is mainly applied to the surface of the Use pots that have drainage holes in theirpotting mix in containers, but it can also be bases, not just at the bottom edges of theirapplied through the drainage holes. side walls. Use pots that are no more than about 20 cm tall. Water will not rise far enoughWater to the potting mix surface up the potting mix in taller containers. Use a potting mix that has a relatively lowIf you have large groups of plants in air-filled porosity. The taller the containerscontainers, you could set up a fixed sprinkler to be used, the lower must be the air-filledsystem and water them from overhead, just as porosity. For 20 cm deep mix, the air-filledproduction nurseries do. There are at least porosity needs to be no higher than 14%;two problems with this. One is that it is now the mix should contain about 20% coirillegal in most parts of Australia, simply fibre dust.because of the second problem: a highproportion of the water misses the containers. The simplest way of watering from below is to have every pot sit in a saucer that is largeThe more usual method of surface watering is enough to hold water for one or more days ofvia a watering wand for plants on patios and plant use. This method is particularly usefulother outdoor areas or via a small watering for indoor plants.can for indoor plants. This obviously takestime and cannot be automated, but there are Another method of sub-irrigation is to placemany advantages. the pot on top of a larger well of water with 13 – WATER FOR PLANTS IN POTS 143
  • 153. Even if you don’t have a self-watering pot, you cankeep an indoor plant alive via wick watering while you For watering by sub-irrigation, there must be plenty ofare away. holes in the base of the pot.a wick (old stocking or other water- Lack of leaching prevents the loss ofabsorbing synthetic cloth) running from nutrients from the mix, so you should useinside the pot through a drainage hole and less fertiliser than you would with wateringdangling in the water in the well. You can from above.set this up yourself by using as a well any But lack of leaching can allow thecontainer that has a lid that is strong concentration of salts in the potting mix toenough to hold the pot. All you need to do get so high that plants are damaged.is to drill a hole in the lid. Water-well pots If your water has a very low concentrationare a commercial variation on this theme. of salts, and you do not use excessive amounts of fertiliser, you should be able toAnother method of sub-irrigation is to sit the maintain a plant with sub-irrigation forpots on capillary matting which is either kept several years before you have any problemsconstantly moist or has water applied to it at with salt.intervals that keep the plants well supplied.This method is a bit trickier to set up than the The saltier your water, the sooner it will beother methods mentioned above, but it works that you need to leach the mix. With anywell for all pots that are no deeper than about sub-irrigation system, you will soon see a20 cm. The capillary matting is installed on white deposit of salts on the mix surface.top of polyethylene sheeting which sits on a They do no harm if they remain there, butflat surface. if the build-up is heavy and starts to move down into the mix, it is time to leach. First,The fact that with sub-irrigation the potting remove the pot from the sub-irrigationmix is not being leached can be good or not system. Then scrape away and discard theso good for your plants, depending on the uppermost 1 cm or so of the mix with itsquality of your water and on how much salts. Pour about two pot volumes of waterfertiliser you use. through the mix. Top up the mix. Return144 GOOD GARDENS WITH LESS WATER
  • 154. it to the sub-irrigation system when drainage has stopped.Fertilisers for plants in containersIf you are going to all the trouble of keepingup a supply of water to your plants growing incontainers, you might as well have themlooking good. You need to feed them,because the potting mix will not do this afterthe nutrients that came with it from the bagare used by the plant or have been washed outthe bottom of the container. Informationabout fertilisers can be found in Gardening A small amount of controlled-release fertiliser makes aDown-Under (see Appendix 1). lot of difference. 13 – WATER FOR PLANTS IN POTS 145
  • 155. Testing environment. Commiphora multijuga (Perfumetree) growing in a crack in limestone.
  • 156. TESTING POT TING MIXESMeasuring the air-filled porosity of a Select a cleaned, undamaged 600 mL milkpotting mix carton and carefully open out the top. MarkThe air-filled porosity of a mix is the the inside of the carton at exactly 12 cm frompercentage of its volume that is air just after it the base. This will usually be just above thehas stopped draining after being saturated height at which the carton had been foldedwith water. Here is a simple way that you can over. Make four holes in its base in positionsmeasure air-filled porosity (see Chapter 13 for such that you can close them with four fingersinterpretation). while holding the carton vertical with two hands. The holes should be about 8 mmNote: This method may look long and diameter, or as big as your fingers will allow.complicated, but it really is very simple. Onceyou get the hang of it, you will take no more 1. Fill moistened mix into the carton rightthan 10 minutes to measure the air-filled to the top. Ideally, the mix should haveporosity of a mix, although that 10 minutes been fairly moist, but not sloppy, for a fewwill be spread over a couple of hours. days before you do this test.You need the following: a cleaned, 600 mL milk carton an electric drill, sharp knife or hole punch of about 8 mm diameter, for making holes in the bottom of the carton a 9 L plastic bucket water (warmed in winter for your comfort) casserole dish or 4 L ice-cream container two pieces of wood or plastic, each of about 1.5 cm square section and about 8 cm long measuring jug of 250 mL capacity calculator. Drilling holes in the base of a milk carton. 147
  • 157. 2. Drop the carton vertically five times onto they seal the holes. Just before final your workbench or other firm surface sealing, make sure that the mix is from a height of 5 cm. This consolidates saturated just to its surface. the mix. If necessary, top up the mix to 8. Raise the carton from the water. about a centimetre above the 12 cm Allow water on the outside of the mark. carton to drip off, while keeping the3. Gently lower the carton of mix into water holes covered. in a 9 L bucket. The height of water 9. Place the carton on blocks in a shallow should be just a few millimetres below the container such as a casserole dish or 4 L top of the mix. Have the water low at the ice-cream container. Remove your start and pour more into the bucket as fingers. Make sure that the holes can needed. Make sure that the mix does not drain freely. Allow water to drain from float up. Leave the carton of mix in the the carton. The base of the carton must water for 30 minutes. be horizontal (any tilting or squeezing4. Carefully remove the carton from the will allow more water to drain out, so water by slowly raising it vertically. Allow giving a falsely high reading of air-filled to drain for a few minutes. If necessary, porosity). add extra mix to the 12 cm mark then 10. Drainage from open mixes will be lower the carton into the water again. complete in 10 minutes, but it could take5. Repeat Step 4. an hour or so from very ‘heavy’ mixes.6. Make a final adjustment of mix height by The water draining from the mix is either adding more mix or gently replaced by air. The volume of air that scraping some out down to the 12 cm enters is the same as the volume of water mark. Lower the carton of mix into the that has drained into the container. water and leave it for a further 10 minutes. 11. After drainage has stopped, remove the7. Reach down through the water and work carton from the blocks, without tilting or your fingers underneath the carton until squeezing the container. Measure the volume of water in the shallow container, or weigh it (1 mL water weighs 1 g). 12. Calculate or measure the volume of carton occupied by the mix. (A 12 cm height of mix in a standard 600 mL milk carton will have a volume of approx. 600 mL). 13. Calculate the air-filled porosity of the mix with the formula: Air-filled porosity (volume %) volume of water drained (mL) × 100Removing the saturated mix. = volume of mix (mL)148 GOOD GARDENS WITH LESS WATER
  • 158. Example: 120 mL of water drains from 18. Weigh the dry potting mix (W3). 600 mL of mix The water-holding capacity of the mix is Air-filled porosity = 120 × 100 = 20% 600 (W1 – W2 – W3) × 100That is, 20% of the volume of the mix was air (W1 – W2)immediately after it had stopped draining. For example, if the wet mix plus carton weighed 800 g, the carton weighed 20 g and the dried mix 380 g, the water holdingWater-holding capacity capacity of this mix is (800 – 20 – 380) 100If you want to know the amount of water held ÷ (800 – 20) = 400 100/780 = 51%. In otherby your mix, all you need to do is this. words, water made up 51% of the weight ofAt Step 11 of the air-filled porosity the just-drained mix.determination, place the carton of drainedpotting mix on kitchen scales. Wettability of a potting mix14. Record its weight (W1).15. Tip all of the potting mix into a large You can check as follows for the need to add a tray. wetting agent to a potting mix.16. Weigh the empty carton (W2). Dry some of the mix by spreading it on a17. Spread the mix out in the tray and sit the piece of paper and leaving it in the sun. tray in the sun until the mix has Fill the dried mix into a small dish, such as completely dried. an aluminium foil pie dish. Make a shallow depression in the centre of the mix with a standard light globe, tennis ball or spoon. Gently add 10 mL of deionised water or rainwater to the centre of the depression. Record the time taken for the water to soak into the mix. The water is regarded as having soaked in when slight tilting of the dish gives no movement of water in the wet patch. Add a wetting agent to the potting mix if it took longer than 20 seconds for the water toTesting the wettability of a potting mix. soak in. 14 – TESTING POTTING MIXES 149
  • 159. APPENDIX 1 SOURCES OF EXTR AINFORMATIONChapter 1 Chapter 2Climate change Australian plantsCSIRO and Australian Bureau of Elliot WR and Jones DL. Encyclopaedia ofMeteorology: www.csiro.au/resources/ps3j6. Australian Plants. Lothian: Melbourne. Therehtml. This site has details on projected effects are nine volumes and some supplements.of global warming on temperatures and Volume 9 will not be published before laterainfall throughout Australia. 2008.Flannery T (2005). The Weather Makers: The Peate N, Macdonald G and Talbot A (2006).History and Future Impact of Climate Change. Grow What Where. (3rd edn). BloomingsText Publishing: Melbourne. Books: Melbourne. This has extensive lists of Australian native plants according to theirHamilton C (2007). Scorcher: The Dirty Politics various requirements.of Climate Change. Black Inc. Agenda:Melbourne. Snape D (2002). The Australian Garden: Designing with Australian Plants. BloomingsIntergovernmental Panel on Climate Change: Books: Melbourne. This is a treasure-trove ofwww.ipcc.ch. This site includes the latest design ideas for Australian gardens.reports on climate change. http://users.chariot.net.au/~hharvey/www.sustainablehouse.com.au. This site APSquery.html. A searchable database ofincludes many ideas for reducing your Australian native plants according to plant‘carbon footprint’ and for maximising type, soil and climatic preferences. It hasrainwater use. been specifically developed for South Australia, but is also relevant to south-westBenefits of urban greenery Western Australia and Victoria.Cooperative Research Centre for IrrigationFutures: www.irrigationfutures.org.au. Mediterranean plantsIncludes forthcoming report: ‘The social and Morgan D (2004). Succulents for Mediterraneanenvironmental benefits of urban irrigation in Climate Gardens. Rosenberg Publishing: Dural.open public spaces and the economic valueassociated with these benefits’. Nottle T (1996). Gardens of the Sun. Timber Press: Portland, Oregon. Nottle T (2004). Plants for Mediterranean Climate Gardens. Rosenberg Publishing: Dural.150
  • 160. This book features many plants that can be Chapter 7grown with minimal extra water. Rain Harvesting, Archerfield, Queensland:Perry B (1992). Landscape Plants for Western www.rainharvesting.com.au. ComprehensiveRegions: An Illustrated Guide to Plants for Water information about tanks and the hardwareConservation. Land Design Publishing: needed to harvest rainwater.Claremont, CA.Savewater®Alliance, Armadale, Victoria: Lists of plants that are suitable forwww.savewater.com.au. Includes a plant particular areasselector for Australia. Association of Societies for Growing Australian Plants: http://asgap.org.au.Windust A (2003). Waterwise House andGarden. Landlinks Press: Melbourne. This has Australian Plants Society, South Australianlists of both Australian and exotic plants of region: www.australianplantssa.asn.au.high drought tolerance. Brisbane City Council: www.ourbrisbane.com. Melbourne Water: www.conservewater.Weeds melbournewater.com.au.Australian Weeds Committee, Launceston,Tasmania: www.weeds.org.au. Ornamental Plant Conservation Association of Australia: www.rbg.vic.gov.au/opcaa. ThisCooperative Research Centre for Australian site maintains collections of ornamentalWeed Management, Adelaide, South plants that might otherwise disappear. YouAustralia: www.weeds.crc.org.au. can purchase rare plants through them.Queensland Government, Natural Resources Renaissance Herbs Pty Ltd (1997): www.and Water: www.nrw.qld.gov.au. Has a list of renaissanceherbs.com.au. This site has lists ofDeclared plants (weeds) for Queensland. herbs according to water needs.Richardson RG and FJ, Meredith, Victoria: Sydney Water: www.sydneywater.com.au/www.weedinfo.com.au. savingwater/inyourgarden/plantselector. University of Melbourne, Burnley College: www.horticulture.unimelb.edu.au/info/ plntdrct.htm. Information about the Burnley Plant Directory. This has descriptions and images of over 3000 plants that are suitable for Australian gardens. Version 2 is due to be released in 2008. The Water Corporation (2003–2006): www. watercorporation.com.au. APPENDIX 1 – SOURCES OF EXTRA INFORMATION 151
  • 161. Chapter 8 Chapter 13Irrigation Australia, Hornsby, New South Handreck K and Black N (2005). GrowingWales: www.irrigation.org.au. Media for Ornamental Plants and Turf (3rd edn). University of New South Wales Press:Smart Approved Water Mark: www. Sydney. This book has extensive technicalsmartwatermark.org. This site lists water- information about potting mixes and therelated products that have been assessed growing of plants in them.independently and approved as being able toreduce water use. GeneralChapter 10 Greenpages Australia, Surry Hills, New South Wales: www.greenpagesaustralia.com.au. ThisAustralian Institute of Horticulture: www.aih. site has extensive lists of companies andorg.au. organisations that can provide products orAustralian Institute of Landscape Architects: information about all things green.www.aila.org.au. Handreck K (2001). Gardening Down-UnderAustralian Institute of Landscape Designers (2nd edn). Landlinks Press: Melbourne.and Managers: www.aildm.com.au. Open Garden, New Gisborne, Victoria:Australian Society of Garden Designers: www. www.opengarden.org.au. This site lists allasgardendesigners.org. Australian gardens that are open for inspection and inspiration over each comingwww.landscapingaustralia.com.au. For links year.to state landscaper associations. Sustainable Gardening Australia, Bulleen,Nursery and Garden Industry Australia: www. Victoria: www.sgaonline.org.au. This site hasngia.com.au. With links to state associations. discussion forums and information aboutwww.plant.id.au. Has a listing of associations many aspects of gardening.related to urban horticulture, with links totheir members.152 GOOD GARDENS WITH LESS WATER
  • 162. INDEXAcacia 27 potting mixes 132, 147–149Actinostrobus 11 anions 56Adansonia grandidieri 9 annual plants 6agave 132 Atacama desert 8aggregates in soils 34–35, 37–39, 47–48, Atriplex 17 58–59, 134 Australian native plants 12, 150air alkalinity tolerance 60 ability to evaporate water 7, 17, 87 drought tolerance 73, 75 as source of carbon dioxide 1, 15–17 fertiliser needs 24 humidity and transpiration 17, 21–22, 68, grasses 110, 120 81, 140 phosphorus needs 26–27 in potting mixes 134, 136 phosphorus toxicity in 62 movement through mulches 96, 100 salinity tolerance 58 source of oxygen for roots 19–21, 29, 34, Australian standard for composts 40 114 Australian standard for potting temperature 81, 142 mixes 132–133air conditioning 3, 7 Australian standard for soils 112air pruning of roots 110 Austrodanthonia spp. 119–121air-filled porosity of potting mixes 135–137 available water 51–53, 112 and sub-irrigation 143 and root depth 46, 48 changing 137 and soil texture 51–52 desirable ranges for potting mixes 135–137 effect of organic matter 51–52 effect of pot depth on 135 held by coir fibre dust 53 measuring 147 held by water crystals 53alkaline soils 21, 27, 56, 60, 112 in potting mixes 131, 135–136alkalinity 58–60 in soil blends 112 effect on trace element uptake by plants 60 from bicarbonate in waters 57, 59–60 backflow prevention 89 of greywater 58, 60–61, 63 Baja California 8 of mushroom composts 42 Banksia audax 13 of water supplies 58 Bauera 27Allocasuarina verticillata 13 Beaucarnea recurvata 94altitude and plant characteristics 8 Beaufortia 27analysis bedding plants 6, 24 of soil 27, 107 Begonia 16 of greywater 61 bentgrasses 119–121 of water 55 bentonite clay 139 153
  • 163. bicarbonate in water 55, 57, 59, 61 camellias 21biennial plants 6 can test 77blood and bone, phosphorus supply by 27 carbon dioxide 1, 39boneseed 14 and gardens 3boron and photosynthesis 15–17, 22 in greywater 63 and plant growth rate 16 toxicity to plants 58–59 as cause of global warming 1Boronia 27 Carpobrotus modestus 102Bossiaea 27 carrots 18Bothriochloa macra 120 cations defined 56Brachysema 27 chewings fescue 119–121bridal creeper 14–15, 18 Chile 8, 10broadleaf carpet grass 122 chloride in water 55–59buckets 85 chlorophyll 10, 16buffalo grass 121–123 chloroplasts 16builders’ rubble 31, 38 Chorozema 27bulbs 9 citrus roots 19 clay 32–34C3 grasses 119 addition to sands 35, 49C3 photosynthesis 17 layers in soils 48, 108C4 grasses 120 clay loam 32C4 photosynthesis 17 clay soilscacti 8, 12, 17 compaction of 47, 128 in pots 73 improvement with organic matter 40, 51, mulches for 100, 103 58 type of photosynthesis 17 improvement with sand 37calcareous soils see alkaline soils improving their structure 36–38, 48, 61calcium nitrate 36 in lawn soils 120, 123calcium in soil blends 112 and soil structure 34, 36–38, 61 planting into 110 as counter to sodium in soils 59 properties 33 effect on sodic soils 37–38 self-mulching 95 in water 55–61 water held by 46, 50–51, 63 sources for sodic soils 36–38 water infiltration into 47, 60, 89, 92,California 10 108Callistemon ‘Little John’ 13 water repellence of 43, 49callistemons 27 waterlogging in 115Callitris 11 climate change 1Calytrix 27 climatic zones, plants from different 7–12CAM photosynthesis 17 Cocopeat see coir fibre dust154 GOOD GARDENS WITH LESS WATER
  • 164. coir fibre dust copper, effect on roots 107 effect on water held by potting mixes 131, corn 17 137–139, 143 Correa 24 water-holding capacity 53 corymbias 27colour couch 120–123 of flowers 7, 15 Queensland blue 122–123 of foliage 7, 10 rooting depth 19, 38, 127 of humus 40 water use by 119 of lawn grasses 126 Crassula rupestris 9 of mulches 96, 102, 141 crassulas 8 of pots 142 crocking 140 of soils 29–31 crop factors 73–78compaction and drip watering 93 how to avoid 47–48 and plant growth 75 of soils 31, 33 how to use 74, 78, 80–82 relieving 107, 124 cruciferous plants 20 under lawns 128 crusts on soils 31, 33–36compost 39–43 and water infiltration rate 31, 47 addition to soils 30, 33 effect of sodium 58, 61 as mulch 95 reduction by mulches 103 Australian Standard 40 cucumbers 23 bark 102–103, 131, 137 cypress 11 for lawns 121, 123–124 in soil blends 112 Dahlia 18 recycling via 3, 15, 112 Darwinia macrostegia 6 water-holding capacity 53 Darwinias 27, 131 weeds in 101 Daviesia 27compost bins 3, 41 density of planting and water use 10, 72compounds, chemical 56 Dianella 10conifers 11 Didierea madagascariensis 101controlled-release fertiliser 24, 66, 133, 145 diggingcontrollers, irrigation 69, 79–81, 89 and soil structure 34, 36, 38, 108cool-season grasses 19, 118–122 effect on plant roots 19 drought tolerance 19 of organic matter into soils 42 mowing and root growth 126–127 wet soil 48, 110 native 119 Disa bracteata 14 planting 124–125 diseases, control by organic matter 39 requirements of 120–121 Dracaena fragrans 69 types of 118–120 drainage water use by 74–75, 118–119 and soil structure 31, 34, 128 INDEX 155
  • 165. effect of layers on 48 mulch requirements 101 excellent needed 9, 57, 114 drought tolerance for lawns 121 and plant characteristics 8–12, 17, 35, 71, improving rate of clay soils 38 73 of potting mixes 134–138, 140–145, 148 of cool-season grasses 19, 127 of soils 50, 115 of warm-season grasses 19, 18, 121–123, pipe 71, 15 127 rate 50 drought-tolerant plants testing 107–108 alternatives to drought-sensitive plants 6, waters 19 117dripper systems 88–94 and mycorrhizal fungi 20 advantages and disadvantages 89–90 and nutrients in mulches 100–101 and drought-tolerant plants 90, 93 and permanent wilting point 51 components 89 and rain 71 controllers for 89 crop factors for 74–76 design 89 drip watering strategy for 90, 92–93 flow rate from 77, 91–92 effect of water stress 23–24, 51, 74 for bucketed water 86 fertiliser needs 24–25, 27, 42, 62, 100–101 for fruit trees 93 mulches for 25, 100–101, 103 for greywater 64–65 rooting habits of 18, 35, 71, 127 for lawns 93, 117, 124 water needs 72, 77–78 for potted plants 94, 143 water use 75 for tank water 71 watering frequency 72, 74–76, 78–79, 127 installation below mulch 19, 99 Dryandra 27 length of run 93 Dryandra formosa 6 run times 77–78, 93 Dryandra tridentate 13 spacing of lines 92drippers earth basins 85, 111 adjustable 91 earthworms and saline water 60, 88 and water penetration into soils 47 compared with sprinklers 87–88 effect on soils 31 for greywater 65, 91 in compost bins 41 patterns of soil wetting from 92 EC see salinity pressure compensating 91 Echinopsis deserticola 9 types of 88–89, 91 electrical conductivity see salinitydrought, effect on plants 8, 22 energy use and global warming 1drought-sensitive plants 51 erosion of soils 113 cool-season grasses 19, 119–120 eucalypts 25, 27 effect of mowing 127 roots 19 effect of water stress on 23, 51 Eucalyptus dolichorhyncha 7156 GOOD GARDENS WITH LESS WATER
  • 166. Euphorbiaceae 17 crop factors for 75Eutaxia 27 drip watering of 93evaporation see also transpiration effects of fertilisers 24 and garden water needs 74–82 effects of water stress 22–24 and plant characteristics 7–12 greywater for 63 and weather conditions 73, 140, 142 in sandy soils 36 effects of mulches 95–98 organic mulches for 25, 101 from pots 66, 135–137, 142 root depth 36 from reservoirs 45 watering frequency 72–73, 82, 90 from soils 50, 73 watering management for 79–80 from sprinkler water 87, 89, 117 FullStop™ device 80 global warming and 1 how to use figures for 74–78 garden plants, weed potential 14 increases salinity 60 garden waste, safe disposal 14 rates 73–74, 74–78 gardening styles 5evaporative cooling of plants 22 gardensevaporimeter 73–74 basic decisions about plants 7evolution of plants 5 benefits of 3–4 design 105ferns 15 how to waterproof 82–83fertilisers new 105–106 acidity from 58, 60 renovation 105 addition to soils 30 size and water requirements 83 and plant drought tolerance 24–27, 42 watering systems for 85–94 and water use by plants 24 global warming 1 controlled-release 66, 110, 133 grasses see cool-season grasses; warm-season effect on water crystals 52, 138 grasses for lawns 121, 123–126, 128–129 gravel for potted plants 132–134, 141, 144–145 as mulch 95, 100, 103, 141 phosphorus toxicity from 26–27 crocking with 140–141 requirements with sandy soils 33 for drainage trenches use at planting 24, 110 for potting mixes 137field capacity 50–51, 66, 80, 90 Great Karoo 8first flush diverters 70 greenhouse gases 1flowering, and water stress 22 grevilleas 21, 27flowers 7 greywater 12, 57–61foliage 7 alkalinity of 58, 60fruit 3, 6, 12 application rates 65–66 effect of water stress 22 application via drippers 64, 65, 89–91fruit trees boron in 58–59, 63 INDEX 157
  • 167. composition 57 effect of earthworms 47 for lawns 118 effect of sodium on 59, 61 how to divert to garden 63–64, 67, 86, for drought-tolerant plants 90 106 for greywater 65 phosphorus in 25, 27, 61–63 for lawns 123–124 potential problems from 61, 65 increasing 47–49 salinity 55, 57 measuring 108 sodium concentrations in 58–59, 61 of soils 47–49, 67, 107–108, 110 storage time 63 instant lawn 120, 125 treatment systems 66 invasive garden plants 14 types 60 ions 56 use during drought 82 effect on soil properties use on gardens 60, 71, 82–83 in water supplies 55–58 use regulations 64–65 iron deficiency 21grouping of plants 73 irrigation controllers 69, 79–81, 89gypsum 36 irrigation systems, amounts of water delivered as source of calcium 36 by 75 effect on sodic soils 37 Isopogon 27 requirement test 37 Jacksonia 27Hakea 27 juniper 11hanging baskets 141herbicides, effect of alkaline water 60 Kentucky bluegrass 119–121hoses, hand held 86 kikuyu 17, 121–123 volume of water delivered 86 Kunzea 27humidity 21 and potted plants 140 landscaping 108 during rain 68 organisations 105humus 29–30, 33, 39–40 soils 112 ability to hold ions 37 lantana 14 and soil structure 34, 39–40 laundry detergents see greywater formation 38 laundry greywater see greywater in potting mixes 132 lavender 13 in soil blends 112 lawn clippings 41, 102Hypocalymma 27 lawn grasses see cool-season grasses; warm- season grassesinfiltration rate 47–48 lawns 117–129 and soil texture 47 cause of patches in 38 and sprinklers 87–88 choosing grass for 118–122 effect of compaction on 48 compaction and 128158 GOOD GARDENS WITH LESS WATER
  • 168. compared with drought-tolerant effect of salts on 57, 60 plants 117–118 effect of sodium on 58–59 crop factors for 74–76, 82 in mulches 100, 102–103 dripper systems for 91, 93 iron deficiency symptoms 21 early care 126 nutrients from 55, 68–69, 101 fertilisers for 128–129 of weeds 14 infiltration rate for 123 phosphorus and 26, 62 installing new 122–125 temperature regulation in 22 moss in 114 variegated 140 mowing 127 waterlogging symptoms 114 phosphorus needs 62, 124 Lechenaultia 27 photosynthesis types in 17 Leptospermum 27 remaking 124 Leucodendron 27 rooting depth 19 Leucospermum 27 thatch in 128 Leucospermum gerrardii 11 trees in 93 life in soils 30 water use by 117 light, and plant growth 1 watering 87, 125–126 loam 32–33 when to plant 124–125 loamy sand 32layers in soils 31–33 Lomandra 10 and waterlogging checking for 124 magnesium coarse sand 48 in potting mixes 133 compacted 51 in soils 37, 56 heavy clay 48 in waters 55, 57–61 infiltration rate 108 Mediterranean-type plants 10 mixing together 107 melaleucas 27leaching Mesembryanthemum 9 of nutrients from pots 144 methane 1 of nutrients from soils 19, 33, 39 Microlaena stipoides 119–121 of salts from soils 33, 36, 58, 60–61, 66 micro-organismsleaves 15–16 and root function 20–21 and drought tolerance 8–10, 12–13, 23–24, and soil structure 34 90 cause water repellence 49, 132, 138–139 and root growth 127 clean greywater 61, 65–66 decomposition of 19, 25, 40–41 control diseases 39 effect of chloride on 58–59 decompose organic matter 38–42, 100 effect of excess boron on 59 fix nitrogen 25 effect of mowing 127–128 mycorrhizal fungi 20, 25 effect of rain on 68, 77 nitrogen drawdown by 42, 132 INDEX 159
  • 169. micro-sprinklers 87–88 Myrtaceae 27Minuria 102Monadenia orchid 14 Namibia 8–9mosquitoes, in tanks 70 native plants, phosphorus needs 26–27mowing 127 new plantings, watering frequency 72 and fertiliser use 128–129 nitrogen frequency 120–121, 123 and drought tolerance 25 height 121, 123 and plant growth 26, 128 of new lawns 126 and root growth 25mulches 85, 95–103 drawdown by woody materials 40, 42, 132 addition to soils 30 for lawns 121, 123, 129 adverse effects of fine 88 from fertilisers 60 and soil structure 103 from organic materials 40, 101 and water evaporation 60, 96, 98–100 in potting mixes 133 and wetting agents 96, 98–100 in rain 68 coarse 98–100 relative to phosphorus 26 compared with soil conditioners 42 nitrous oxide 1 effects of 103 non-wetting soils see water repellence fine 98–100 nutrient deficiencies, iron 21 for cacti and succulents 100–101 nutrient supply 33 for drought-tolerant plants 25, 100–101 for fruit trees and vegetables 101 orchid seeds and mycorrhizal fungi 20 for potted plants 141 organic matter 39–43 inorganic 95, 97 and nutrient leaching 39 mineral 95 and soil structure 34, 36, 38–39 myths about 95 and water infiltration rate 47 nitrogen drawdown by 42 and water repellence in soils 42 on leaf surfaces 13 as mulch 100–101 organic 95–96, 98–100 benefits of adding to soils 36–37, 39 over dripper lines 19, 65, 88–89 disease control by 39, 65 protect soil 47, 114 effect on plant roots 39 quality and water losses 46 effect on water-holding capacity of standard 40 soils 39–40, 46, 51–52 thickness 95, 98–101 from plant roots 20 types 95 increasing its content in soils 40, 100 under cacti 9 in soils 30–32, 40, 100, 112 use at planting 42, 109, 111 potential problems for soils 42 water held by 77, 86, 88, 98 organic mulches see mulches, organicmushroom composts, soluble nutrients in 42 ornamental plants 23mycorrhizal fungi 20, 25 crop factors 75160 GOOD GARDENS WITH LESS WATER
  • 170. fertiliser needs 24 C4 17, 120 watering frequency 72 CAM 17over-watering prevention 136 pine trees 11Oxalis 14–15 plant growth rate and carbon dioxide 16oxygen and water supply 16 needed by roots 19–21, 34, 114 plant roots see roots produced by photosynthesis 3, 15–16 planting 107, 124–125 supply in potting mixes 136 how to 110 use of water crystals during 53Pachypodium rosulatum var. gracilius 17 plants 5–27pansy 6 and water 5parsley 6 damage by phosphorus 24–27, 42, 62–63,pathogens, in organic materials 42 110, 133Patterson’s Curse 14–15 damage by salinity 57–60pavers, porous 68 damage by sodium and chloride 59, 61pea straw 102 density of planting 10Pelargonium spinosum 6 drought tolerance and water needs 72–73peperomias 8 drought tolerance characteristics 8–12perennial ryegrass 119–121 effects of alkalinity on 59–60perennials, definition 6 effects of water stress 22permanent wilting point 23–24, 51 evolution of drought tolerance 5pH 21, 27, 113, 121, 123 for alkaline soils 21phosphate, in water 55 ground cover 103phosphorus 26–27 grouping for water use efficiency 73 and drought tolerance 25 in pots 131–145 content of laundry detergents 61–63 list of salt–tolerant 58 for lawn grasses 119, 121, 123–124, 129 minimising their use of water 74–75 from humus 40 preparing for planting 110 in greywaters 61 quality and water use 74 in mulches 25, 101 response to climate 7–12 in potting mixes 133 staking 111 in poultry manure 42 water quality and 66 need at planting 110 water use by 12 storage in roots 18 watering frequency 72 toxicity from greywaters 61–63 plastic sheeting 103 toxicity to plants 24–27, 42, 62–63, 110, 133 P/N ratio of fertilisers 26, 129 uptake by mycorrhizal fungi 20 poplar 12phosphorus-sensitive plants 25–27 population 1photosynthesis 15 Portulacaria afra 8 C3 17, 118 potassium, deficiency 69 INDEX 161
  • 171. potatoes 18 median values for cities 76pots, effects on plant roots 107, 109 systems for storing 68potted plants 131–145 use of stored during drought 82 drippers for 94, 143 rain switches 79 fertilisers for 133, 145 recycling 3, 25, 40–41, 106 sub-irrigation of 94, 143–144 redgrass 120–123 temperature effects 142 reeds 20 ways of watering 94, 143 reservoirs 1–2, 45, 55 when to water 141 in pots 72, 141potting mixes 131–145 in soils 45–53, 60 air supply in 134–136 Rhagodia 17 air-filled porosity 135–137, 147–149 rhododendrons 21 analysis 132 roots 12, 15–16, 18–21 effect of alkaline water 58, 60 and dripper systems 91–93 effect of coir fibre dust on water held and mycorrhizal fungi 20 138 and soil physical properties 33–34, 38, 40, effect of water crystals on water held 138 48, 59, 113, 123, 128 non-standard 134 circling effects 107, 109–110 properties 134 deeply penetrating 10, 18, 71 standard 132–133 diseases of 39, 73, 141 water repellence in 138–140, 149 effect of mulches on 97, 100–101, 103 water-holding capacity 135, 149 exclusion of 78, 91, 93 wetting agents for 138 extent 6, 8, 10, 16, 19, 35–36, 46, 51, 71, 86,poultry manure, phosphorus supply by 27 90, 118 soluble nutrients in 42 function 16, 18, 34, 42pressure reduction, for drippers 89 growth in lawns 38Protea 27 growth in sandy soils 35Protea exemia 11 need of oxygen 19, 103, 114, 136Pultenea 27 nitrogen effects on 25, 128pumps 64, 71 of lawn grasses 118–121, 123, 127 of succulent plants 8Queensland blue couch 122 protection of 21, 42 quality in pots 107, 109, 131, 136–137, 142rain 1, 67–71 salinity and 58–59 and plant growth 16 suckering 12 as source of nitrogen 68 surface 10, 18 benefits of 68 temperature and 142 diversion from roofs 69–71 uptake of nutrients by 15–16, 21, 34, 51, 60 infiltration into soils 67 uptake of water by 15, 18, 86, 90, 126–127 making the most of 67 roses 24162 GOOD GARDENS WITH LESS WATER
  • 172. salinity 55–57 reservoir size in 50 and lawn grasses 120–122 rooting depth in 26, 35 and potted plants 66, 138, 142, 144 salinity effects in 57, 60 and soil moisture sensors 80 texture determination 32 and watering systems 88 use of water crystals in 53, 110 damage to plants 57–60 used for lawns 121, 123, 128 effect on water held by water crystals 52, water repellence in 43, 49 138 Santa Ana couch 38 effects around drippers 88, 90 SAR see sodium adsorption ratio effects on soils 37, 58 sawdust 102 from controlled-release fertilisers 66 Scaevola aemula 132 interpreting readings 57 seashore paspalum 121–123 leaching from soils 33, 66 sensors, of soil moisture 79–80 measuring 57 silty clay loam 32 of composts 40, 42 snails 101 of poultry manure 42 sodic soils 37, 58–59, 61, 112 of swimming pool water 57 sodium adsorption ratio, defined and of water for plants in pots 66 interpreted 58 of water supplies 36–37, 55–57, 61, 68, sodium readings, interpretation 57 damage to plants by 59 reduced by rain 68 damage to soils 58 units 55–57 in greywaters 58, 61saltbushes 17, 20 in softened waters 59Salvation Jane 14–15 in water 55–56sand 32 interpreting analytical figures 58 as a mulch 95, 100–101 soil analysis 27, 107 for improving clay soils 36–38 pH 56 in soil blends 31, 112 soil blends 112 layers in soils 31, 48, 107 soil colour 31sandy clay 32 soil conditioners 100sandy clay loam 32 see also organic mattersandy loam 32 soil depth, and water held 45–46, 51–52sandy soils soil moisture sensors 79–80 amounts of water held in 47, 50–52 soil pH 33 dripper spacings in 90, 92, 124, 126 and plant growth 21 improving their structure with clay 34–35 soil structure 34–38, 112 infiltration rate 47 and infiltration rate 47, 114 pH change in 60 and organic mulches 103 phosphorus toxicity in 26, 63 and oxygen supply to roots 19 properties of 33 benefits of good 34, 60 INDEX 163
  • 173. damaged by sodium 58, 61 spinifex 10, 18 effect of sodium 58–59 sprinkers 87–88 improving 35–40 advantages and disadvantages 87 looking at 30–31 compared with drippers 86–87 poor 34, 115 fixed 87soil texture 31–33 losses of water during use of 87 and dripper watering 92 not for greywater 65 and soil properties 33 on hoses 87 and water held 47, 51 pop–up 88 for lawns 123–124 stomata 10, 21–22 grades 32, 112 and water shortage 22 of layers in soils 48 effects of water shortage 23soil type, and water held 46 function 16soils 29–38 structure of soils see soil structure amounts of water held 51 Stylidium elongatum 101 application of wetting agents to 49 sub-irrigation, of potted plants 143–144 as reservoirs of water 45–53 subsoil 30 compaction under lawns 128 succulent plants 8, 73 composition 29–30 mulches for 100–101 contamination with builders’ rubble 31 type of photosynthesis 17 crusts on 31 sugar cane 17 erosion 113 sugarcane mulch 102 field capacity 50–51 sulphate, in water 55 for lawns 123 swimming pool water salinity 57 how they hold water 46 Syngonium 13 improvement with organic matter 39 increasing their organic matter content 40 tall fescue 19, 118, 120–121 infiltration of water into 47–49, 107–108 tanks layers in 31, 48 for storing rainwater 68–71 leaching salinity from 60 mosquitoes in 70 odour 31 tap timers 79 pH 124 temperature properties 29–30 in pots 142 salinity effect on plants 58 of air 21–22 waterlogging 113–114 terracing 49, 114 wettability 49 testingsorghum 17 for response to calcium 36South Africa 10 of potting mixes 147–149spacing between plants 10 texture see soil textureSpanish moss 12 thatch 128164 GOOD GARDENS WITH LESS WATER
  • 174. Thryptomene 27 availability see available waterThyrptomene maisonneuvii 10 costs 69Tillandsia usneoides 12 effects of supply on plant growth 74toadstools 20 evaporation and mulches 96–100tomatoes 22 held by mulches 98topsoil 30 increasing amount held in soils 51 saving before building 106 infiltration into soils 107–108total alkalinity see alkalinity, of water supplies minimising use by plants 74–75transpiration 21 rate of evaporation 73–74trees 7 recycling to gardens 106 planting 107 requirements for gardens of differenttropical plants 8 sizes 83tubers 9 retention around young plants 85 salinity 57vegetables 3, 6 use by different types of plants 12, 75 and greywater 63, 65 water crystals compost for 40, 42, 101 amounts of water held in soils 53 crop factors for 75 effect of salinity on 52 drippers for 93 in potting mixes 138 effects of fertilisers 24–25 use at planting 53, 110–111 in sandy soils 36 use in sandy soils 53 mulching 102, 114 water in soils 46 watering frequency 72–73 water meters, use of 76–77 water needs 22, 78, 80, 82, 90, 118 water quality 55–66 water repellenceWallaby grass 119–121 from organic matter 43warm-season grasses 120–123 in potting mixes 138 crop factors 75 in soils 49–50 drought tolerance 19 of mulches 98–100 photosynthesis type 17 of sandy soils 35 requirements of 122–124, 127 overcoming in potting mixes 138–140 root depth 19 water restrictions 1 types of 120–123 water salinity 55 water use 74–76, 118–119 water softeners 59 water use by 118–119 water stresswater and water use by plants 23 amounts delivered by irrigation benefits of 23 systems 75–77 effect on plants 22 analysis 61 water use as greenhouse gas 1 by plants 22 INDEX 165
  • 175. by different lawn grasses 119 weeds 14–15 effects of fertilisers on 24 effect on other plants 111water-holding capacity growth in mulches 101 increased in soils by organic matter 39–40, in compost 41 46 weeper hoses 91 of potting mixes 135, 149 Weeping grass 119–121 of soils of different texture 46 Welwitschia mirabilis 9watering cans 85 wettability, of potting mixes 149watering systems 85–94 of soils 49 see also buckets; sprinklers; drippers wetting agents, effect on mulches 98–100watering, frequency for different types of use before planting 110 plants 72 use in potting mixes 138 of lawns 125–126 use on soils 49–50 of new plants 111 wetting front detector 80 of plants in pots 131–145 Widdringtonia 11 strategy 78 wilting 23 using crop factors 78 wind, and transpiration 21 working out a schedule 72–79 Wisteria 12waterlogging 31 detection 114 zinc overcoming 115 toxicity from manures 41waterproofing a garden 82–83 uptake by mycorrhizal fungi 20weather station data 81 Zoysia 121–123166 GOOD GARDENS WITH LESS WATER