This Slideshow Will Introduce You to Five Basic Aspects of Home Composting
Thomas Richard, Robert Kozlowski, Nancy Dickson and Roger KlineJuly 1989
Composting converts waste, leaves, kitchen scraps and garden wastes, into a valuable product which, when used in the garden, results in healthier plant growth when added to garden soil.
Composting can also help solve our society's solid waste disposal problem. Food and yard waste comprise over 30% of our solid wastes nationwide.
Decomposition is a natural part of the nutrient cycle of living things. Composting is simply human intervention to enhance and accelerate the decay process.
Composting is a microbiological process. Many organisms have evolved to use decaying matter as their food source. Bacteria are among the simplest and most common organisms. Single-celled and microscopic, they are found almost everywhere in the environment. Although they are too small for us to see, they are responsible for most decomposition. (Special thanks to David Emerson).
Mites and other soil invertebrates feed on bacteria and fungi, helping to keep their populations in check. Competition among the different organisms insures that only the most efficient decomposers multiply. (Substitution - slide not available in electronic form).
Earthworms are perhaps the most familiar decomposer. By blending soil and organic matter in their digestive track, they produce stable, nutrient-rich aggregates that improve the structure of soil. (Substitution - slide not available in electronic form. Special thanks to Seattle Tilth Association).
All decomposers are bound together in a complex feeding web. They turn organic wastes into a usable humus for the soil. (Substitution - original slide not available in electronic form).
While the natural process of decomposition will occur without any assistance from us, several factors can be managed to accelerate the compost process. (Substitution - original slide not available in electronic form).
Organisms utilize carbon as a source of energy and nitrogen to grow and reproduce. Without enough nitrogen, there will be few microorganisms, and decomposition will be slow. If there is too much nitrogen in the compost, some of it will turn to ammonia that will volatilize, creating an odor.
The optimum C:N ratio is about 30 to 1. This ratio will make fast, hot compost. Grass, animal manures and fresh green plants are high in nitrogen.
Leaves, brush, sawdust and wood chips are all good sources of carbon. Blending these carbon sources with nitrogenous materials can provide a satisfactory C:N ratio.
Surface area is another key factor to consider. Since decomposition is a microbiological process, it occurs in thin films on the surface of particles. A large particle has less total surface area than the same particle chopped into small pieces. Therefore if particles are too big, the process will take longer. A one-inch wood chip will decompose much slower than grains of sawdust. An easy way to shred fallen leaves is to mow them before raking.
Decomposer organisms need water also. The decomposition process will slow down with either too much or too little water. The optimum moisture content for compost is about 40 to 60 percent, damp enough so that a handful feels moist to the touch, but dry enough that a hard squeeze produces no more than a drop or two of water.
Most microorganisms active in composting require oxytgen to live. Their "aerobic" activity forms carbon dioxide and heat as by-products. If too little oxygen gets into the compost, the process can become "anaerobic." This condition results in foul odors. The by-products of anaerobic decomposition include methane and hydrogen sulfide gas. Hydrogen sulfide smells like rotten eggs.
Oxygen will move into the pile if it is loose and there is plenty of space between particles, as when straw is mixed in the pile. Finer material may need to be aerated by physically turning the pile with a pitch fork or a compost turning tool. With the rapid decomposition that occurs with high nitrogen materials, turning the pile becomes necessary to prevent anaerobic conditions from developing.
Heat will be given off as organisms feed on wastes and break them down into less complex molecules. Ideal temperatures for composting are between 90 and 150 degrees Fahrenheit. High temperatures can help kill weed seeds and disease organisms, but temperatures above 150 degrees Fahrenheit will also kill the decomposers and slow the process.
Bacteria reproduce very quickly and are naturally present in air and soil, so there is usually no need to add them to the compost pile. Of the many inoculants, or compost starters available, the best is a handful of freshly made compost.
Almost any type of organic material can be composted, but some are especially easy to manage in a home composting pile. While most leaves are fairly high in carbon, maple leaves have a C:N ratio near the optimum level of 30:1. With the right moisture and frequent turning, maple leaves can break down in just a few weeks time.Oak leaves have a C:N ratio of about 60:1, and also have high levels of tannins which are resistant to decay. Mixing these leaves with a high nitrogen materials will accelerate their decomposition.
Brush can compost or be used as mulch if chipped to a reasonable size. Because wood chips have a high C:N ratio, and large particle size, they will break down relatively slowly. A better alternative is to spread them on paths or use as mulch, easily recycling them to the landscape. Chips are often available free from arborists and utility companies.
Fresh grass clippings are high in nitrogen, about 20:1. By themselves they are too wet and will mat, creating unpleasant anaerobic odors. But they will compost well when mixed with a carbon source such as leaves or brush. (Special thanks to Seattle Tilth Association.)
Short grass clippings are better left on the lawn, where they will decompose and return nutrients and organic matter to the soil. Contrary to popular opinion, clippings will not contribute to thatch buildup.
Clippings from home lawns treated with pesticides may contain chemical residues. With few exceptions, these residues will not persist from one growing season to the next. If the type and level of pesticide used is unknown, those materials should not be added to the compost pile.
Manures are high in nitrogen, about 20:1, and contain many organisms helpful to the compost process. While horse and cow manure are fine to add to the compost pile, dog and cat litter may contain parasites which can cause human disease.
Other more exotic materials may be available for composting in your area. These aquatic weeds, while a problem for water recreation, make excellent compost if dried out a bit. Food processors may also have by-products that are suitable for composting. (Special thanks to David Stern).
Coarse material, such as corn stalks, small tree and shrub limbs, can also be composted. Shredding these materials increases the surface area that organisms can work on which significantly decreases the time required for composting.
Yard wastes can be composted using a variety of systems including holding units, turning units and mulching. Food composting systems include incorporation, vermicomposting (composting by earthworms), and turning units.
Many different options are available to contain your compost. One option is a holding unit in which wastes are accumulated. After materials are added to the holding unit they are left undisturbed to slowly decompose. Snow fence can make a simple and movable holding structure.
Used pallets are often available for free from manufacturers. Tied or nailed together, they effectively contain compost in a stable structure.
Moving compost from bin to bin on a weekly basis will make rapid compost and provide considerable strenuous exercise! The turning unit method is used to make compost quickly and is more suitable for food wastes. Compost is turned frequently to provide aeration.
Rotating drums take some of the work out of turning, and are available from garden supply stores. Such units often represent considerable investment for the volume of material composted.
Perhaps the easiest way to compost food waste is to bury it in the garden or yard. Bury food waste at least six to eight inches deep to keep animals from digging it up. Care should be taken not to damage the roots of nearby plants.
Recycling food and yard waste can provide a host of benefits for the garden. Compost incorporated in the soil provides limited nutrients to plants. However, the organic matter it provides can significantly improve soil structure, allowing better drainage in heavy clay soils and improved water retention in light sandy soils. (Special thanks to Seattle Tilth Association.)
Screened compost can be blended with soil and peat and used as a growing media for containerized plants. A simple screen can be made with hardware cloth and a wood frame.
Coarse, partially decomposed compost can also be used as a mulch. Mulches are useful for water retention and weed control, but have a cooling effect on soil and will delay maturity of warm weather crops.
Fresh compost should not be used for germinating seedlings. The use of sterilized soil is preferred because many seedlings are susceptible to disease pathogens. Compost that has aged for at least a year is less of a problem, and may prove beneficial in preventing damping off disease. (Special thanks to Nancy Trautmann.)
Home composting provides households with the opportunity to efficiently convert waste material into a valuable soil amendment. The ultimate result of the process is a healthier, more productive and easier to maintain garden. Our challenge is to change residents' values toward waste disposal and make them aware of alternative disposal practices. Home composting offers the opportunity for residents to contribute to the solution themselves and receive a beneficial product for their own gardens.