Composting

The processes that occur within a compost heap are microbiological, chemical, and physical. Microorganisms break down the carbon bonds of organic materials in the presence of oxygen and moisture, giving off heat in the process.

High temperatures can be achieved most easily in a compost heap that is built all at once and tended regularly. Enclosed bins, often used by city gardeners, may produce humus within a month. An open heap, such as in the back corner of a garden, will probably achieve lower temperatures, but it will still eventually decompose. However, a year or more may be required to produce humus, and it will contain some undecomposed materials. In northern winters, the composting process will slow down and almost stop except at the core of a large, well-arranged heap.

The byproducts of composting can also be used. Some composters run water pipes through their compost heaps and utilize the heat generated to warm greenhouses and even houses. The methane given off can also be collected and used as a fuel called biogas for cooking.