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Backyard
composting |
When man in pursuit of the gentle art of horticulture harvests fruits and vegetables, prunes trees and shrubs, rakes leaves and grass, and clears plant debris from the garden at season's end, he interrupts the natural cycle of growth and decay whereby plant life is sustained. By removing the nutrient-rich matrix of organic matter from yard and garden, whether as harvest or as "waste," he deprives the soil of its principal natural source of humus. While synthetic fertilizers, fashioned from non-renewable petrochemicals, may replace the lost nutrients, they do nothing to replenish the precious one percent by weight of organic matter in the soil which increases water-holding capacity and improves tilth. By composting and returning the humus to the soil, man completes the natural cycle which he has interrupted through other horticultural practices.
Composting recycles nutrient-rich organic matter which would otherwise use up to twenty-five percent of valuable landfill space or pollute the air if burned. Only about eleven percent of earth's ice-free land surface is arable, and new soil forms at a rate of one centimeter every one hundred to one thousand years. If we are to save our biosphere and ourselves, we must move to sustainable horticultural practices and stop wasting the organic materials which keep our soils fertile. Backyard composting is a simple step which we can all take to help insure that our species has a future.
The basic ingredients in any compost heap are organic matter and moisture. Leaves, grass clippings, vegetable peelings and animal manure are all examples of organic matter. A compost pile can also benefit from the addition of wood ashes, sawdust, used potting soil, coffee grounds and many other readily available materials.
The key to successful composting is in combining materials to provide the proper physical conditions. Nitrogen from green garden debris (grass clippings, vegetable scraps) provides microbes with their basic body-building proteins, while dry debris from carbon sources (autumn leaves, sawdust) is used as an energy source and moisture regulator. Because some of the carbon is lost as carbon dioxide, and is present in cellular material in a greater quantity than nitrogen, much more carbonaceous than nitrogenous material is needed for fast decomposition. Layering the materials is an easy way to arrive at the correct ratio. Use a six to eight inch layer of dry matter, then a two inch layer of green matter. Top this with a sprinkling of soil or animal manure to innoculate the pile with bacteria and other microorganisms. Continue layering, moistening with water as you go. Try to maintain the moisture content of a wrung-out sponge.
The mass of moist organic matter you have created will soon begin to heat up. You can speed the decomposition process by shredding the materials, and by turning the pile every few days to boost the oxygen level and bring the cooler materials from the outer edges to the center. The compost should be ready to use in a few weeks to a few months, depending on your method.
A basic heap should measure at least a cubic yard (three feet by three feet by three feet) to ensure that enough mass exists to hold the heat once decomposition begins, while piles larger than five feet cubed may not allow enough air to reach the microbial action in the center and are difficult to turn. Material can be accumulated as it becomes available, or assembled at one time by using leaves from neighboring yards (you might offer the neighbor some finished compost in return),asking supermarkets or restaurants for vegetable scraps, or visiting a farmyard to collect animal manure. If the slower accumulation method is used, you may wish to cover each addition with soil or turn the materials occasionally to reduce problems with odors and flies.
Minerals are heavily concentrated in leaves due to absorption by deep tree roots. Leaves are also valuable for their textural addition to soil. Dry leaves should be crushed or shredded to speed decom-position and to prevent blowing and matting. Leaves can be used as a mulch without first composting. You may wish to add a nitrogen supplement before mulching to avoid a deficiency. Oak leaves make an especially good mulch or compost for acid-loving plants such as azaleas and blueberries. Avoid the use of black walnut leaves because of the presence of juglone, a substance which hinders crop plant growth.
Lawns can absorb nutrients from decomposing grass clippings that are left on the lawn after mowing. Because of their abundance and high percentage of nitrogen, clippings can also be put to good use on more heavily cropped plots. It is nitrogen which provides the heat source to activate a compost pile. To prevent compaction, mix the grass with a large amount of dry material, or first allow the grass to dry before adding it. Garden debris and weeds can be used if weed seeds and perennial weed plants are avoided, and fibrous materials (corn stalks, broccoli stems) are first chopped or crushed. Sticks and twigs are best used as a mulch after chipping, or as aeration layers in compost heaps. Sawdust and wood chips (avoid treated lumber) decompose slowly and must be mixed with a nitrogen source in a compost heap. They can provide an absorption layer and structural strength to the heap. Research is being conducted to determine to what extent herbicides break down in composted yard and garden wastes. If you are concerned with this issue you may wish to completely avoid herbicide-treated sources.
Most kitchen scraps are valuable to composting because of the variety of nutrients they contribute. Coffee grounds contain nitrogen, phosphorus, potassium and trace elements. Tea leaves contribute similarly, and can be easily disposed of by composting the filter bag at the same time. Crushed eggshells are mostly calcium. Banana and citrus peels are a source of nitrogen, phosphorus and potassium. Do not use grease, as it will delay degradation of other materials by its coating action. Bones and meat scraps should be avoided because of their slow decomposition and risk of luring animals. No nut shells except peanut should be composted unless a special pile is reserved for slow-to-decompose materials.
Manure can contribute a variety of nutrients and bacteria. If straw or sawdust is used as animal bedding, nearly all of the nutrients are preserved that were not used by the animal. Farms and riding stables are usually glad to furnish individuals with all the manure needed for a home composting operation.
Thin layers of soil or previously made compost can innoculate a heap with the necessary organisms to start the decomposition of new materials. Soil can also prevent the loss of nitrogen in the form of ammonia, and provide moisture and heat insulation if the pile is covered with a one to two inch layer.
Wood ash is a source of potassium and can help to neutralize mixtures containing a large quantity of acidic materials such as oak leaves.
Some optional materials useful for adding to compost mixtures can be obtained at garden centers. Greensand is an undersea deposit containing nearly all the elements which occur in sea water, and is especially rich in potassium. It will stimulate bacterial action in a compost heap. Phosphate rock is useful in preserving nitrogen because of its ability to combine with ammonia. Its benefits double if a test shows your soil to be deficient in phosphorus. Lime was until recently thought a necessary ingredient to a well constructed compost pile because of its ability to neutralize the acidity that exists when organic materials start to decompose. Although an acid condition is present at the beginning of the process, the finished compost is essentially neutral to slightly alkaline. Too much lime can cause a loss of nitrogen as ammonia.
Sir Albert Howard, recognized as the creator of organic gardening, is credited with developing the first scientific approach to composting. He devised the Indore Method while working as an agronomist in India in the first third of this century. Through experimentation and by duplicating nature, Howard found that three times as much plant matter as manure was needed for the finest product. His method began with a five to ten foot wide layer of brush to provide aeration, over which was spread a six inch layer of green material, then a two inch layer of manure, and smaller layers of topsoil, lime, and rock powders. All layers except the brush continued until a height of approximately five feet was reached. The completed pile was insulated from drying winds by tamping the surface and covering the pile with soil. By turning the pile after six and twelve weeks, Howard had finished compost in three months.
In 1949, the Sanitary Engineering Department of the University of California devised a way of making compost in only two weeks. The secret to the 14 Day Method is to first finely shred all materials. This will form more surface area for microbial activity, and provide better aeration and moisture control. If the heap does not begin to heat up during the first day, more nitrogen should be added. The heap is ready to turn after three days, a job made easier by the shredded materials. Continue turning at two to three day intervals, checking the moisture content each time. The internal temperature should begin to drop after twelve to fourteen days, at which time the compost is usable.
The No Turn Method, originated by F. W. Bassett, is based on elevating the heap over an open framework which allows air to pass through the pile as it heats up. These convection currents force cooler air from ground level to rise, thus aerating the pile and eliminating the need to turn the materials. Moisture control is one problem that may arise, and air channels may cause uneven aeration of the materials. It is recommended that no weed seeds or diseased plants be used with this method.
Sheet composting allows the gardener to put fresh materials directly into the soil by tilling under or spading in leftover stalks, leaves, and mulch when production ends for the season. This method puts more bulk and nitrogen into the soil, and releases minerals more slowly than other ways of using compost. Replanting of the area can take place as soon as one to two months. Trench composting is similar, in that fresh materials are incorporated into the soil. A trench the length of the garden bed is filled with organic matter, tamped down, watered, covered with manure, then mulched. Gardeners can plant directly in the mulch, but a nitrogen deficiency may develop unless topsoil is used in place of the manure. Trench composting can cause areas of anaerobic activity, and decomposition is slow. Green manuring is the growing of cover crops such as buckwheat, clover, and alfalfa specifically for use as sheet compost. These crops are generally planted after a food crop has been harvested, and turned under six weeks before replanting. A sizable area is needed to rotate food and green manure crops, but an added benefit is that the rotation will discourage plant and insect diseases.
Vapors of carbon dioxide and nitrogen can be lost from an aerated compost pile as oxidation takes place. Anaerobic composting reduces the loss of nutrients by processing the materials without air. A simple way to construct an anaerobic heap is to till or spade the soil surface to encourage earthworm movement, then form an above-ground ridge using compostables. Soak with water and cover with black plastic. Soil should be placed around the edges to make it airtight. The compost will be finished in two to three months. You may then plant directly in the compost, or use it elsewhere in the garden.
While not as rich a source of nutrients as compost, leaf mold is an excellent source of minerals and useful as a mulch. Moistened autumn leaves can be contained in a bin and left to rest over the winter. A crumbly mulch will be available by summer of the following year. The American Association of Nurserymen suggests this method for making a small quantity of anaerobic leaf mulch: fill a clear plastic bag with a bushel of shredded leaves, two gallons of water, and five pounds of high-nitrogen fertilizer. Close the bag and place in a sunny area, turning the bag every other day, for usable leaf compost in three to five weeks.
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