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GOOD GARDENS WITH LESS WATER
GOOD GARDENS WITH LESS WATER    K EVIN H AN D RE CK CSIRO PUBLISHING GARDENING GUIDES
© Netherwood Horticultural Consultants Pty Ltd 2008All rights reserved. Except under the conditions described in the Austr...
CONTENTSPreface                                         viiAcknowledgements                                ix 1      Cause...
Grevillea ‘Superb’ is a showy cross between G. banksii and G. bipinnatifida that is best suited to warm temperateareas.
PREFACEDuring the last 10 years or so, gardening in much      as the global warming to which we allof Australia has become...
easiest for you as their carer, and for them, if         source of carbon dioxide, without which thereyou have chosen only...
ACKNOWLEDGEMENTSThis book was initiated by my publisher – Ted      Queensland; Jon Lamb, Jon LambHamilton – of CSIRO Publi...
A major cause: people and their machines. (Photo: Ted Hamilton)
C AU S E S O F WAT ER                      S H O R TAG E SThere are three major causes for the current        rainfall acr...
50.0                                                                                        40.0                          ...
slight decrease in average distance                   suggested that there should be an ‘oxygen   travelled by private car...
Also, by creating a pleasant setting for their                                        home, gardeners increase its value b...
PL A N T S A N D WAT ER        KEY POINTS        Types of plants        How to select plants that are suited to your clima...
Pansy – an annual plant.roofs and recycled from within the house.Much of any stored rainwater might well beused for produc...
the term ‘perennial’ is generally restricted torefer to clumping herbaceous plants whosetops die back after flowering, but...
Climatic zones with very high                                                        evaporation potential and little wate...
Plants of extreme deserts (from top): Echinopsisdeserticola cactus in the Atacama (Photo: EleanorHandreck); 1500-year-old ...
often vertically oriented, with high oil             In some areas, such as the western slopes ofcontent, thickened, often...
A dryland plant from seasonally cold areas: juniper.                                                         Actinostrobus...
Table 1. Rough guide to the drought tolerance of different types of plants Plant characteristics                          ...
Some of the many leaf forms (clockwise, from top left): Syngonium, thin, 150 mm; Banksia audax, thick and hard,70 mm; Drya...
INVA SIVE GARDEN PL ANTS More than three-quarters of Australia’s weeds           produce seeds that stick to clothing and ...
Bridal creeper is smothering less bushland since the introduction of a fungal biological control agent. roadsides or over ...
growers often enrich the air inside their                                                      greenhouses from the curren...
THREE T YPES OF PHOTOSYNTHESISC3 photosynthesis This is the type of                  same time. This means that the stomat...
store food, for the plant’s later use (as in                                                        carrots) or for the ne...
Surface roots take up nutrients being recycled from      The shallow roots of citrus need to be protected –decaying leaves...
WHY ARE MYCORRHIZ AL FUNGI USEFUL? Plants have extensive root systems, but these             crucifers (cabbage, cauliflow...
do this (e.g. rhododendrons, camellias, many                                                     hybrid grevilleas) show s...
Path of water through a plant.Temperature and water use                        them, and they are never short of nutrients...
end rot and cucumbers to become bitter.Fruit trees may drop much of their fruit.Some benefits of water stressWe can use wa...
Fertilisers and water use by plants                                                           This book is about water and...
recycling from fallen leaves will usually                 However, there are two situations in whichprovide all they need ...
PHOSPHORUS SUPPLY If you have any connection with farming, you will        allow excessive build-up of phosphorus in your ...
Any fertiliser applied to these plants must have a                                                       P/N ratio of less...
Patterns in the soil. (Photo: Eleanor Handreck)
KNOW YOUR SOIL        KEY POINTS        Getting to know your soil        Soil texture and soil structure        Improving ...
5.    Living organisms – ranging in size from      small animals to viruses.Soils look and feel different because:     the...
4.    Can you see a layer of topsoil above soil          limited supply of water. Fine soil over a      of different appea...
HOW TO DE TER MINE SOIL TE X TURE Moisten some of your soil in your hand with a                   Form the moist soil into...
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
Good Gardens With Less Water - Australia
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  1. 1. GOOD GARDENS WITH LESS WATER
  2. 2. GOOD GARDENS WITH LESS WATER K EVIN H AN D RE CK CSIRO PUBLISHING GARDENING GUIDES
  3. 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. 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. 5. Grevillea ‘Superb’ is a showy cross between G. banksii and G. bipinnatifida that is best suited to warm temperateareas.
  6. 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. 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. 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. 9. A major cause: people and their machines. (Photo: Ted Hamilton)
  10. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 37. Patterns in the soil. (Photo: Eleanor Handreck)
  38. 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. 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. 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. 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

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