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TREES & Plants

Composting

Composting is a biological process whereby plant material, such as leaves and grass clippings, and other sources of organic matter decompose into humus – a dark brown, crumbly mass resembling rich garden soil. Composting does exactly what nature does all the time by recycling valuable nutrients for reuse. For the home gardener, it offers the opportunity to recycle yard and kitchen wastes while avoiding the expense and effort of disposing of these materials. The resulting compost can be applied as a soil amendment, top dressing, or mulch.

WHY COMPOST?

compost pile
As more communities restrict the dumping of yard waste in landfills, this encourages homeowners to compost their leaves, grass clippings, and other yard debris. The incorporation of organic matter, or humus, in garden and landscape soils is a necessity often overlooked by gardeners. Organic matter helps maintain a steady supply of plant nutrients, especially nitrogen and potassium. It also improves the soil’s ability to absorb rainfall or irrigation water and to reduce surface runoff, yet holds nutrients loosely at the optimum, slightly acidic pH so they’re easily released into the soil to meet plant needs. Adding compost to soil increases earthworms and soil microbial activity that benefits plant growth.

WHAT MATERIALS CAN BE COMPOSTED?

Most of the ingredients for the compost pile are raw materials from the garden, grass clippings, sod, leaves, hedge clippings, weeds, and discarded plants. Kitchen scraps such as fruit and vegetable trimmings can also be added to the pile. Do not include grease, fat, meat or bones because they are slow to decompose, will cause odors, and attract rodents. Small twigs and branches of trees or shrubs should be cut up before adding to a compost pile, to speed up the time of decomposition. Sewage sludge and animal waste is not recommended for use in compost, because it may transmit certain diseases and contain toxic amounts of heavy metals such as cadmium and lead. Also, diseased plant material or weeds that have gone to seed should be avoided. Usually the compost pile is contained in some type of enclosure, although it can be made without one. There are commercially available compost bins made of slatted metal, plastic or plasticized wire mesh. Perforated trash cans may also serve the purpose, or simple containers can be constructed of galvanized wire fencing, boards, bricks or concrete blocks. It is important that there be enough openings to allow adequate air movement. The compost pile should be located in a visually unobtrusive area and where odors from possible anaerobic decomposition would not be a nuisance. A properly functioning compost pile has no unpleasant odor, but you can get a smell going by dumping on a layer of matted, wet grass clippings that doesn’t break down properly. When compost forms, heat is produced. The pile should have a minimum volume of 1 cubic yard, which is 3 feet by 3 feet by 3 feet, to facilitate its internal temperature reaching 150 to 170 degrees. The heat will kill weed seeds, insect eggs, and disease organisms present in the raw material. If the pile is much larger, the air necessary for decomposition will not enter the pile and will need to be turned frequently for the center of the pile to decompose sufficiently

compost pile
CONSTRUCTING A COMPOST PILE

The compost should be constructed in layers. Alternate moist and green materials like grass clippings or kitchen wastes with dry materials such as leaves or cornstalks. A pile built primarily of dry materials will decompose very slowly, because it lacks nitrogen and water. Compost that is made primarily of fresh, green materials will decompose very rapidly, but will shrink as water is lost, leaving only a small volume of compost. Therefore, combining equal volumes of dry to moist is optimum. If the organic materials seem dry, enough water to promote decomposition should be added. Chopping the materials into smaller pieces is not necessary, but doing so will greatly increase the rate of decomposition, because the microorganisms have more surface area to work on. This is especially true for coarse, dry ingredients. Another method of constructing a compost pile, perhaps the one most commonly used, is to alternate layers of plant material and garden soil. Begin by placing a 6 to 8-inch layer of organic matter inside the composting container. The microbes needed for decomposition are already present in this organic matter. The addition of a 1-inch layer of garden soil will speed the process. Continue building the pile with alternate layers of soil and organic matter as they accumulate throughout the growing season.

MAINTAINING A COMPOST PILE

The organisms that break down the organic matter also require large amounts of nitrogen for rapid and thorough decomposition of the plant material. Therefore, 1 pound of a complete fertilizer (10-10-10) or 1/3 pound of ammonium nitrate (33-0-0) may be added to the pile for each cubic yard of compost. Cottonseed meal or dried blood may be used instead of the above concentrated fertilizers, but this will result in somewhat slower decomposition activity. To hasten the composting process, keep the pile moist but not soggy. Inadequate moisture will reduce microbial activity, while excess moisture may cause undesirable anaerobic decomposition and unpleasant odors. The pile can also bemoistened occasionally with a garden hose during dry periods. As the plant materials decompose, the pH of the pile is lowered, meaning that its acidity is increased. However, as the process continues, the pH eventually rises to the neutral level of 7.0 pH. A pile that is built in layers, as described above, should be turned for the first time about 4 weeks after its construction. A spading fork or similar tool can be used to ‘turn’ the pile by lifting the pile’s lower layers on top of the upper layers in order to mix the contents. The mixed pile is less dense, maximizing the contact with oxygen necessary for aerobic decomposition. Locating two or three compost bins side by side can make the turning process easier and simpler; just shift the material from one bin to the other. During the warm months, the pile should be turned about once a month. In cooler weather, decomposition is slower and during the winter, very little decomposition occurs. A well-managed compost pile will break down in 4-6 months. Problems will develop if the pile is not working properly. These problems include unpleasant odor, slow decomposition, a dry pile, or standing water. The solution to a problem depends on its cause. In general, turning the pile, adding water, maintaining a mixture of dry and moist materials, or adding nitrogen will solve the problem.

USING COMPOST

compost pile
Compost is ready to use when it is dark and crumbly and the ingredients have lost much of their original identity. Finished compost should have an earthy, pleasant smell. Once it is ready, the compost can be used as surface mulch on plant beds. Apply compost 2-4 inches deep around vegetable and perennial plants to control weeds and conserve moisture. As a soil conditioner, compost can be mixed into the soil just before planting to lighten heavy soil and improve drainage, or it can increase the moisture holding ability in sandy or light soil. Adding compost to soil increases earthworm and soil microbial activity that benefits plant growth. Compost can also be used as a substitute for peat moss to amend soil in potting mixes, seed flats, or when transplanting trees and shrubs.