Composting

The most heat is given off at the beginning of the composting process, when readily oxidized material is decomposing. Digestion of the materials by bacteria is strongest at that time. Later, the temperature within the pile decreases, and the bacterial activity slows down, though it continues until all the waste is digested. Other microorganisms take over as the heap cools.

Microorganisms, such as bacteria, protozoa, fungi, and actinomycetes (the latter resemble both bacteria and fungi), work to change the chemistry of the compost. They produce enzymes that digest the organic material. Bacteria are most important initially and fungi later. If the pile is not turned regularly, the decomposition will be anaerobic and produce foul-smelling odors. By turning the pile, a gardener creates conditions for aerobic decomposition, which does not produce odors.

Some organisms work on the compost pile physically instead of chemically. They tend to arrive only after the pile has cooled to normal air temperature. These organisms include mites, millipedes, sowbugs and pill-bugs (isopods), snails and slugs, springtails, and beetles. Finally, the worms—nematodes, flatworms, and earthworms—do their part. These animals eat and digest the organic materials, adding their nutrient-filled excrement to the humus. In addition, they give off substances that bind the material in granules or clumps. The movement of these animals, especially earthworms, through the material helps to aerate it.