Composting ❂ 6G ardeners have long made and used compost to improve garden soil. Today, we also compost plant and vegetable matter because it is an important wayto reduce the amount of waste that is burned or dumped in ❂ Topics in this chapterlandfills. Yard wastes and kitchen scraps can make up 20 ❂❂ The science of compostingpercent or more of household garbage. Composting effec- ❂❂ Managing the decay processtively recycles that waste. ❂❂ How to make compost Some people think that composting is not possible inAlaska because of the cold temperatures and the short ❂❂ Health and safety questionsgrowing season. Of course, that is not the case. Decom- ❂❂ Using compostposition occurs naturally in Alaska forests with organisms ❂❂ Composting food wastesadapted to colder temperature. In Alaska, gardeners can ❂❂ Composting and thespeed up the composting process by following the same sci- environmententific principles that are used in other parts of the country.Composting is the science of controlling the decompositionprocess. There are two types of composting: aerobic and anaero-bic. The organisms responsible for aerobic decay requireoxygen or a well-aerated pile. Aerobic decay happensquickly and generates heat. The temperatures are highenough to kill weed seeds and pathogens. Many nutrientsare retained in the compost produced. Anaerobic compost-ing is done by organisms that do not require oxygen to live.It is a slow process, smells bad and nutrients are lost tothe atmosphere as gas. Thus, the goal of the gardener is tofocus on the aerobic method. By Craig G. Cogger, Extension Soil Scientist, Washington State University; Dan M. Sullivan, Extension Soil Scientist, Oregon State University; and James A. Kropf, Extension Agent, Pierce and King Counties, Washington State University. Adapted by Michele Hébert, Extension Faculty, Agriculture and Horticulture, Cooperative Extension Service, University of Alaska Fairbanks.
114 • Composting—Chapter 6 It is broken down into carbon dioxide and The science of composting water and releases nutrients to plants in the process. The cycle of growth and decay Composting carries out part of the earth’s Fast (hot) composting biological cycle of growth and decay. Plants The decay process can be manipulated or grow by capturing energy from the sun, controlled to make it proceed quickly. TheSee Chapter 3,Soils and carbon dioxide from the air, and nutrients key is to balance food, water and air in theFertilizers. and water from the soil. When plants, and compost pile to favor the growth of thermo- animals that eat them die, they become raw philic (heat-loving) microorganisms. These materials for the composting process. In organisms are the bacteria. The by-product other words, once dead, organisms decay or of microbial activity is heat. When condi- decompose. tions are favorable for high-temperature Microorganisms, fungi, insects, worms, microorganisms, compost piles heat rapidly mites and other creatures (Figure 1) convert to 120° to 150°F. The high temperature kills the carbon from dead plants into energy for most weed seeds and pathogens (disease their own growth, releasing carbon diox- organisms). Once the hot phase is complete, ide into the air (Figure 2). Similarly, they lower-temperature microorganisms, worms, recycle nutrients from decaying plants into insects and other invertebrates complete the their own bodies and eventually back into decay process. the soil. Other plants and microorganisms use the carbon and nutrients released by the Slow (cold) composting composting process, and the cycle begins If you do not maintain ideal conditions again. for hot composting, microorganisms still The material that remains from the decay break down wastes. Decay is slower, cooler process is humus, a form of soil organic and less effective at killing weed seeds and matter. It holds water and nutrients in the pathogens. soil and makes the soil more porous and easier to dig. Once in the soil, humus is fur- ther decomposed by soil microorganisms. Managing the decay process You can affect the speed of the compost process and the quality of finished product by managing the environmental factors. These include the raw material or food, moisture, air and organisms. The compost pile can be thought of as food and home for Actinomycetes Fungi Bacteria microbes. The management goal is to make the conditions in the compost pile ideal for Figure 1.—Primary groups of microorganisms the growth of microbes. involved in composting (magnified more than 1,000 times). (Reprinted by permission from On- Farm Composting Handbook, NRAES-54, Natural Food (raw materials) Resource, Agriculture and Engineering Service, For fast composting the initial mix must Cooperative Extension, 1992: 607-255-7654; www. provide a rich food (energy) source for nraes.org.)
Chapter 6—Composting • 115 Organic matter (including carbon, Water Heat CO2 chemical energy, protein, nitrogen) Minerals (including nitrogen and other nutrients) Organic matter (including carbon, chemical energy, Water Compost pile nitrogen, protein, hu- mus), minerals, water, microorganisms Microorganisms Raw materials Finished compost O2Figure 2.—The composting process. The amounts of carbon, chemical energy, protein and water in thefinished compost are less than in the raw materials. The finished compost has more humus. The volume of thefinished compost is 50 percent or less of the volume of raw material. (Reprinted by permission from On-FarmComposting Handbook, NRAES-54, Natural Resource, Agriculture, and Engineering Service, CooperativeExtension, 1992:607-255-7654; www.nraes.org.)the bacteria. Table 1 shows some materi- alfalfa hay and deciduous leaves. Theseals commonly used in making compost. materials are handy for ensuring the successThey are separated into energy materials of hot compost piles.(nitrogen sources), bulking agents (carbon Mixing bulking agents with energy sourc-sources) and balanced materials. es provides the right balance of moisture, air Energy materials provide the nitrogen and nutrients for rapid composting. A mix-and high-energy carbon compounds needed ture of one part energy source with two partsfor fast microbial growth. If piled without bulking agent (by volume) usually gives abulking agents, these materials usually are reasonable mix for rapid composting.too wet and dense to allow much air intothe compost pile. When you open the pile, it Particle sizewill have a foul, “rotten egg” smell. The smaller the particles size the more Bulking agents are dry, porous materials surface area for microbial activity and thethat help aerate the compost pile. They are quicker the raw material will be able totoo low in moisture and nutrients to decay decay. Grinding, cutting, smashing or chop-quickly on their own. ping raw materials reduces particle size. Hot Balanced raw materials have both energy composting requires a relatively uniformand bulking agent properties. These materi- particle size of ⅛ to ½ inch in diameter.als compost readily without being blended Small particles do limit the amount ofwith other ingredients. Examples include air that can be moved into a pile. Bulkinghorse manure mixed with bedding, spoiled agents are added to increase air movement.
116 • Composting—Chapter 6 High carbon material such as wood chips squeeze water out of it with your hands. At can be screened out of finished compost dry times of the year, you may need to add and be reused several times to increase air water. In rainy winter locations, a pile may movement. not heat up unless you cover it to keep out rain. Mixing Contrary to popular opinion, layering is Aeration not the best way to build a pile. If all of the The microorganisms responsible for fast materials are on hand when you build the decomposition need oxygen. The pile needs pile, mix them thoroughly throughout the to be porous enough to pull in outside air pile. If materials accumulate over time, add to replenish oxygen as it is used. Including new materials to the center of the pile. This bulking agents in the mix creates a porous practice helps aerate the center of the pile, pile. As the pile decomposes, it will settle, where anaerobic conditions are likely to reducing aeration. Turning the pile or add- occur. ing more bulking agents improves aeration. Pile size Microorganisms The pile must be big enough to hold heat. Raw materials used to form a compost A hot pile decays much faster than a cold pile usually contain all the microorganisms pile. Small piles usually are colder because needed to make compost. You do not need they have small cores that hold less heat. to add soil or compost starters with special Small piles also dry out faster. A pile of microorganisms. The best source of micro- about 1 cubic yard is big enough for com- organisms (if needed) is finished compost. posting, even in Alaska. Nutrients Moisture Just like people, microorganisms need All materials in the pile must be moist but nutrients (such as nitrogen, phosphorus not soaking wet. Check moisture when you and sulfur) to grow and reproduce. These turn the pile. The mixed material should nutrients occur in the raw materials used in feel moist, but you should not be able to the compost mix. Additional fertilizer from any source (organic or inorganic) usually is not needed. How to make compost You do not need a bin or other container to make compost. Piles work well. How- ever, some people prefer containers because they look neater, or because it is easier to shield them from pests. Containers can be simple or fancy. Make them from materials such as old pallets, lumber, mesh fencing or cinder blocks (Figure 3).
Chapter 6—Composting • 117Slow (cold) composting Employing slow composting is an easyand convenient way to turn yard wastes intoa useful soil amendment. It often is the bestmethod for people who do not have the timeto tend a hot compost pile. Simply mix non- Figure 3.—Some people compost in open piles; others prefer usingwoody yard wastes into a pile and let them bins.sit for a year or so. Microorganisms, insects,earthworms and other decomposers willslowly break down the wastes. A mixture of One option is to bury vegetable andenergy materials and bulking agents pro- fruit wastes directly in your garden. Dig avides the best food source and environment hole or trench about a foot deep, add a fewfor decomposition (see Table 1). inches of wastes, mix them with the soil Add fresh wastes by opening the pile, and refill the trench with soil. Another wayplacing the wastes in the center and cover- to avoid pests is to compost fruit and veg-ing them. This helps aerate the pile and also etable wastes in a worm bin (described laterburies the fresh wastes so they do not attract in this chapter).pests such as flies, dogs and bears. Slow composting does not produce the Fruit and vegetable wastes are particu- heat needed to kill many weed seeds. It islarly appealing to pests, so be sure to bury best to pull and compost weeds before theythese wastes within the pile. If pests are still go to seed. If you put seeds in the composta problem, you may need to screen the pile pile, be prepared for more weeding.or use another method of composting thesewastes. Fast (hot) composting If you create and maintain a balance of air, moisture and energy for compost mi-Table 1.—Compost raw materials. croorganisms, they produce a hot pile thatEnergy materials(High moisture, low porosity, high nitrogen) breaks down quickly. The heat kills manyGrass clippings weed seeds and disease organisms. MakingFresh dairy, chicken or rabbit manure hot compost takes extra effort, but it pro-Fruit and vegetable waste duces a high-quality product quickly.Garden trimmings One method for making hot compost isBulking agents described below.(Low moisture, high porosity, low nitrogen, high carbon) Building the pileWood chips 1. Collect enough material to make a pileSawdustGrass hay at least 1 cubic yard in volume. (AnWheat straw open pile 5 feet wide at the base by 3Balanced raw materials feet high holds about a cubic yard.)(Low to medium moisture, medium porosity, Use roughly two parts bulking agent to medium nitrogen and carbon) one part energy material (see Table 1).Horse manure and bedding Chop, shred, mow or smash coarse ma-Deciduous leavesLegume hay terials so they will break down faster.
118 • Composting—Chapter 6 Health and safety questions Are there any plant materials to keep out The amount of turning and monitoring re- of a compost pile? quired is difficult for even the most avid If you are composting by the slow home composter. The simplest way to method, keep diseased plants and seed avoid potential pathogen problems is to heads of weeds out of your compost keep manure out of your compost pile. pile. For any compost, avoid coarse, If you do use manure, avoid applying woody materials because they break the compost where you grow high-risk down slowly and make the pile hard to crops such as lettuce or carrots. Careful turn. washing or peeling does remove most Some plants contain compounds that pathogens. Thorough cooking is even slow microbial decay. Western red cedar, more effective at killing pathogens. often used for fence posts because of Keep dog, cat and pig manure out of its resistance to decay, can break down your compost pile and garden. Some of slowly in compost piles. the parasites found in these manures can Can a compost pile catch fire? survive even the most thorough compost- A compost pile will ignite only if it ing process and remain infectious for has a very hot zone next to a dry zone. people. Fires do not start in moist or small piles. Are herbicides a problem in compost? Can I use manure in my compost? Some people are concerned If you use fresh manure in a slow that herbicides (weed kill- compost pile or directly in your garden, ers) in compost-amended soil See Chapter 20, a small risk exists that disease-causing might harm plants. Most her- Weed pathogens will contaminate garden bicides in home compost piles Management. vegetables. The risk is greatest come from lawn clippings. for root crops (such as carrots The warm temperatures in a compost pile and radishes) or leaf crops (such accelerate herbicide breakdown to non- as lettuce), since the edible part toxic compounds. Binding with organic touches the soil and often is not matter in the compost also inactivates cooked. herbicides. Breakdown and binding You can’t be assured that reduce the risk of herbicide damage. To pathogens are killed unless you avoid herbicide problems: carefully monitor temperatures • Use few (or no) herbicides. in your compost pile. To ensure • Return treated grass clippings to the pathogen kill, the pile must lawn rather than composting them. reach temperatures greater • Use herbicides that break down than 130°F and must be quickly. turned often. Turning the pile • Let your compost sit for a year or moves cooler material from more before using it to allow nearly the edges into the hot center. complete breakdown of herbicides.
Chapter 6—Composting • 1192. Start the pile by adding energy mate- What if hot compost isn’t hot? rial and bulking agent. Then mix with a If your pile isn’t hot, do the following: pitchfork. • If the pile is dry, add more moisture.3. Squeeze a handful of the mixed material • If the pile is mostly bulking agent, add to check its moisture level. If you can energy materials or nitrogen fertilizer. barely squeeze out a drop of water, the • If the pile is too wet, add more bulking moisture level is ideal. If the pile is too agent. Cover the pile or build a larger dry, add water and check the moisture pile during the rainy season. again. If it is too wet, mix in some drier • If the pile has a foul smell, try turning material. it more often or adding more bulking4. Continue adding energy material and agent to increase the amount of air. bulking agent, mixing and checking • If the pile is too small, try building a moisture until the pile is built. larger pile to hold heat better.Turning the pile Sometimes you may have several prob- Use a pitchfork to turn the pile weekly, lems to overcome. If you cannot get the pileand add water when needed. Turning gets air to heat, all is not lost. The pile eventuallyinto the center of the pile and speeds decay. will break down by the slow method.It also mixes material from the outside of thepile into the hot center. Cover the pile during Using compostrainy periods so it will not get too wet. The best part about compost is the ben-Curing efit it provides your garden. Mix compost After initial mixing, a regu- with soil to add organic matter, or use it aslarly turned pile usually stays mulch.hot (120° to 150°F) for several See Chapter 3,weeks. It will shrink to about Soils and Amending soilhalf its original volume by the Fertilizers. Well-decomposed, earthy composts areend of this time. good soil amendments. They make soil The pile then needs to sit another 4 to 8 easier to work and create a better mediumweeks to cure. Curing affects the availabil- for plant growth. You can mix 1 to 2 inchesity of nitrogen and the microbial activity of of compost into your soil before you plant athe compost. Uncured compost may harm vegetable garden, lawn, flower bed or coversome plants, especially when compost is crop.used in potting soil or to start seeds. Curingis less critical when small amounts of com- Mulchingpost are worked into soil. With two compost Composts applied to the soil surfacepiles, you can let one batch cure while you help control weeds, conserve water andstart another batch in the second pile. protect soil from erosion. The best time to Temperatures during curing are 80° to apply compost mulches is in early sum-110°F. The compost is ready to use when at mer, after plants are established and theleast 8 weeks have passed since initial mix- soil has warmed. Later, the mulch can being, the pile no longer heats when turned dug or tilled into the soil. When mulchingand the material looks dark and crumbly. perennial plantings, choose compost made
120 • Composting—Chapter 6 from woody bulking agents; it decomposes ded in 1-inch-wide strips and mixed with slowly, resists compaction and slows weed peat moss make excellent bedding. Worms establishment. need some grit for breaking down their food. Add a little topsoil for this purpose. Put the worms in the bedding with their first feeding. Composting food waste Moisture Composting kitchen scraps in an outdoor In order to survive, worms require 75 to bin sometimes attracts pests. Some people 90 percent moisture content in both their prefer using worm composting, as described bodies and their bedding. To achieve this below. percentage, add 3 pounds of water for each Worm bins pound of dry bedding (a ratio of 3:1). An easy way to check the moisture content of Many food wastes can be composted in bedding is to squeeze some in your hand. worm bins. Examples include fruit (not cit- If a few drops of moisture are released by rus) and vegetable peels, grains, pasta, baked squeezing, the bedding is sufficiently moist. goods, coffee grounds and even coffee filters. If five or more drops are produced, the bed- Do not add meat or dairy products. ding probably is too wet. Place worm bins where temperature and moisture can be controlled. An ideal Kinds of worms to use temperature range for worms is from 55° The red worm used in a box environment to 77°F. Worms also need a moist envi- is Eisenia foetida. These red worms feed on ronment. Air circulation is a must in and the surface of organic matter. around a worm box. Choose a location that Nightcrawlers and other garden earth- is convenient for maintaining the box. worms are very important for soil improve- The size depends on how much waste ment, but won’t survive in a worm box. you generate per week. A box measuring 1 Earthworms live only in furrows in the soil. foot by 2 feet by 3 feet can handle 6 pounds Number of worms of kitchen waste per week, which is about The number of worms required depends average for a family of four to six. on the daily weight of food waste added. Since worms can eat their own weight in Starting a worm bin food in 24 hours, measure worms by weight Colored rubber containers are popular as rather than number. Two pounds of worms worm bins because they are lightweight. are needed for each pound of kitchen waste Worms avoid light, so the container should added per day (a ratio of 2:1). For example, be dark inside and have a good lid. The lid if you produce 3½ pounds of kitchen waste should cover the top but does not need to at- per week (½ pound per day), use 1 pound of tach securely to the container. There should worms. Calculate as follows: be air holes somewhere on the container — 3½ lb kitchen waste per week either on the lid or sides. If you use a plastic ÷ 7 days in a week bin, be sure to add both drainage and aera- = ½ lb waste per day (average) tion holes. Never use a container that has ½ lb waste per day x 2 lb of worms for been used for storing toxic chemicals. each lb of daily waste Start by putting bedding in the worm box. = 1 lb of worms Corrugated cardboard and newspaper shred-
Chapter 6—Composting • 121Red worm sources for a longer time, make arrangements with Check with your local Extension office or someone to feed your worms.the Internet. Changing the beddingWorm bin management After many weeks, you will notice that the bedding is disappearing as worms andAdding waste microorganisms decompose the material. It is a good practice to vary the location The color of the bedding also becomeswhere you bury wastes in the worm box. darker. As these things happen, the favor-A worm box 2 feet by 2 feet has approxi- able environment for the worms decreases.mately nine locations where you can bury Large amounts of accumulated castingskitchen wastes. That gives you nine feed- might become harmful to the worms, sinceings before you have to bury again at the castings of one worm are toxic to otherfirst location. worms. Decide when to change the bedding Grinding is not necessary because kitchen based on the condition of the bedding andwastes break down very quickly. Do pulver- the quantity of worms in the box.ize egg shells, however. Population controlLeaving the box untended Worms multiply fast. Avoid overpopula- If you need to be away from home, just tion. Use extra worms to start a new wormfeed the worms a little extra and leave box or give them to someone else who isthem undisturbed. They can go 3 weeks or starting a worm composting box.a month without feeding. If you go away Commonly asked questions about worms Can a worm see? ingests the food along with a grinding No, worms don’t have eyes. However, material such as sand, topsoil, or lime- they are very sensitive to light, and they try stone. Contractions from muscles in the to hide as soon as they are exposed to light. gizzard compress the particles against Where is the worm’s mouth? each other, thus mixing them with fluid The worm’s mouth is in the first ante- and grinding them into smaller pieces. rior segment. There is a small protruding Do worms need air? lip just over the mouth. When the worm Worms need a constant supply of is foraging, this lip stretches out to sense oxygen from the air. The oxygen diffuses food. across the moist tissue of their skin, from Does a worm have teeth? the region of greater oxygen concentra- Worms have no teeth for chewing their tion (air) to that of lower concentration food. They grind food in their gizzard by (inside the worm). muscle action. How do I use worm compost? How does a worm grind his food? Use worm compost like any other A worm can take only a small particle compost. Sterilizing is not necessary. of soft, moistened food in its mouth. It
122 • Composting—Chapter 6 Odor and pest control Control odors by not overloading the box For more information with waste, keeping out inappropriate waste and providing adequate fresh bedding. Do UAF Cooperative Extension not fill the bin with a lot of food waste until publications the worm population is established. Never Composting with Worms, HGA-01020. add cheese or other animal products to any Composting in Coastal Alaska, HGA- type of composting system. 01021. Fruit flies are more of a nuisance than The Compost Heap in Alaska, HGA-01022. a serious problem. Minimize fruit flies in Worms in a Tote, HGA-01025. a worm bin by completely covering fresh food waste with several inches of bedding Other publications and by covering the bedding with a sheet of Rangarajan, A., E.A. Bihn, R.B. Gravani, newspaper, cardboard or plastic tucked in D.L. Scott and M.P. Pitts. 2000. Food around the edges. Safety Begins on the Farm: A Grower’s Guide. Cornell Good Agricultural Prac- tices Program, Cornell University Col- Composting and the lege of Agriculture and Life Sciences. environment Backyard composting reduces the flow of wastes to landfills or burn piles and pro- duces valuable organic matter for the soil at the same time. The composting process is fueled by the solar energy captured in plant tissue. The benefits are the same whether you compost in carefully tended hot piles or in neglected slow piles. Backyard com- posting is a simple, yet important, way to improve our communities and the environ- ment.