A centuries-old process for converting organic materials like vegetative debris into a valuable soil amendment, composting benefits soils and plants physically, chemically, and biologically.
Composting is the controlled, aerobic (with oxygen) biological decomposition of organic materials at temperatures high enough to kill weed seeds and plant (and human) pathogens. It is essentially a manufacturing process: Organic wastes like landscaping debris, food wastes, and so forth are feedstocks to the process, millions of beneficial microbes are the workforce, and a humus-rich soil amendment is the product.
The key to successful compost manufacturing is to create the most favorable working environment for the microbes and higher-order organisms doing the work. Like all workers, these decomposers need air, water, and food. Air comes from keeping the compost pile aerobic, first by properly mixing compost ingredients and then by periodic turnings/ remixings or by blowing air into a pile with a fan or blower.
Water for microbial growth comes from the feedstocks themselves, although much water is lost due to evaporation from the heated compost pile. This lost moisture must be replaced to maintain optimum conditions.
Microbial food comes from two abundant elements: carbon (C) and nitrogen (N). The ratio between C and N (between 25:1 and 35:1) is achieved by mixing feedstocks together in the right ratios (just like mixing ingredients to bake a cake).