When is the compost finished?

There is no fixed time to produce finished compost. Duration depends on feedstocks, composting method
used and management. It can take as little as three  months and as long as two years. Compost is considered finished when the raw feedstocks are no longer actively decomposing and are biologically and
chemically stable.  Some practitioners refer to finished compost as stable; refering to the state of biological
activity. Maturity is usually defined as the degree of humification (conversion of  organic compounds to
humic substances, which are most resistant to microbial breakdown). It is easier to measure compost
stability than maturity, so most composters measure temperature or compost respiration (oxygen
consumption). When the temperature at the center of the pile returns to near-ambient levels and oxygen
concentrations in the middle of  the pile remain greater than 10-15% for several days, compost is considered
stable or finished. These measurements should betaken when the compost pile has at least 50% moisture
content by weight.It is important to learn how to assess the maturity or stability of the compost because stability will affect many of  the chemical and biological properties of  the compost, and ultimately how the compost can be used.“Stability indices” and maturity/stability testing are available from compost research and education organizations (see Resources). Immature or biologically unstable composts can be used on farms as a soil amendment ONLY IF applied several months prior to planting. Immature composts can also be used in site remediation, and as land fill covers.