Composting

Composting uses microorganisms to transform organic materials such as plant residues, food scraps and yard trimmings. In managed systems the process is usually aerobic, meaning oxygen is supplied to the decomposing material. Microbes use carbon-rich material as an energy source and nitrogen for growth; their activity releases heat and carbon dioxide while converting the feedstock into a more biologically stable product. This differs from unmanaged decomposition in oxygen-poor conditions.

Effective composting depends on a suitable balance of carbon-rich and nitrogen-rich ingredients, along with adequate moisture, oxygen, particle size and temperature. Dry leaves and woody materials tend to provide carbon, while fresh plant matter and food scraps are often nitrogen-rich. Cornell's compost chemistry guidance describes about 30 parts carbon to one part nitrogen by weight as a general starting ratio, while noting that the availability of the materials' carbon can alter how quickly microbes can use it. Turning or otherwise aerating a pile replenishes oxygen; too little oxygen can lead to anaerobic conditions and unpleasant odors.

Composting can be carried out at home, in community programs, on farms or at larger centralized facilities. A backyard pile is a simple option; vermicomposting uses worms in a managed bin to process suitable organic scraps. Larger facilities handle defined feedstocks and control process conditions. Commercial compost products often use thermophilic processes, in which high temperatures help reduce pathogens. Accepted materials vary by facility, so local collection rules matter.

Finished compost is used as a soil amendment in settings such as gardens, farms, landscaping and green infrastructure. Adding organic matter can support soil structure, plant growth and moisture retention, and can help reduce erosion and runoff. Diverting organic waste from landfills also avoids some methane that can arise when it decomposes in oxygen-poor landfill conditions. These benefits depend on producing and using suitable, uncontaminated compost; compost is not a universal substitute for other soil management practices.