Materials for composting
Many organic materials are suitable for composting. Yard wastes, such as leaves, grass clippings, straw, and nonwoody plant trimmings can be composted. The dominant organic waste in most backyard compost piles is leaves. Grass clippings can be composted; however, with proper lawn management, clippings do not need to be removed from the lawn (see Alternatives to Composting Grass Clippings, page 12). If grass clippings are used, it is advisable to mix them with other yard wastes such as leaves or wood chips as a bulking agent to increase free air space. Otherwise, the grass clippings may compact and restrict air flow. Branches, logs, and twigs greater than 1/2-inch in diameter or more than 8 inches long should be put through a shredder/chipper first. Kitchen wastes such as vegetable scraps, fruit waste, coffee grounds, and eggshells may also be added. Some cities have ordinances that restrict the use of food scraps in compost piles. Check with local authorities about restrictions in your area.
Because they may pose a health hazard or create a nuisance, certain organic materials should not be used to make compost. Adding human, cat, or dog feces cannot be recommended because they may transmit diseases. Meat, bones, grease, whole eggs, and dairy products should not be added because they can attract rodents to the site. Most plant disease organisms and weed seeds are destroyed during the composting process when temperatures in the center of the pile reach 130-150 degrees F for 15 days or longer. However, in most home compost piles, it is very difficult or impossible to mix Materials for Composting efficiently enough to bring all wastes to the center. Consequently, adding large amounts of weeds with seeds or diseased plants may create problems if the compost is used in the garden.
Sawdust may be added in moderate amounts up to a maximum of 10% of the total pile volume, if additional nitrogen is applied and free air space is adequate. Approximately 1-1.5 lb. of actual nitrogen (6-9 cups of ammonium nitrate) is required for 100 lbs. of dry sawdust. Wood ashes act as a lime source and if used should only be added in small amounts (no more than 1/2 cup per five gallon bucket). Excessive amounts of wood ashes will result in loss of nitrogen from the pile. Ordinary black and white newspaper can be composted; however, the nitrogen content is low and paper will therefore slow down the rate of decomposition. If paper is composted, it should not be more than 10% of the total weight of the material in the compost pile. We recommend recycling newspaper through appropriate community recycling centers rather than through backyard composting.
Examples of other organic materials that can be used to add nutrients, especially nitrogen, to the pile include cotton seed meal, blood and bone meal, livestock manure, and lake plants.
Avoid composting plants that have been treated with herbicides or pesticides. Small amounts of herbicide-treated plants (e.g., grass clippings) may be mixed in the pile as long as you are careful to let them decompose thoroughly. Studies have shown that low levels (less than 0.1 parts per million) of 2,4-D, diazinon, and pendimethalin can be detected in well-composted yard trimmings2. This level, however, is less than 1% of the level typically found in yard waste mixtures prior to composting and is not considered a risk for using in the garden. Ideally, clippings from lawns recently treated with herbicides should be left on the lawn to decompose (see section on Alternatives to Composting Grass Clippings). Both pesticides and herbicides are degraded at varying rates. A list of common chemicals used on the home lawn and their degradation rate in soil is provided in Table 1. Even if some treated grass clippings are used, the degradation of these chemicals in a properly maintained compost pile should be at least as fast as that in the soil.
Table 1. Persistence of herbicides in soil3
|Common name||Trade names||Persistence in soil (months)|
|Glyphosate||Roundup, Kleenup||Less than 1|