Tom Richard
Cornell Cooperative Extension
Operator's Fact Sheet #5 of 10
Cornell Cooperative Extension
Operator's Fact Sheet #5 of 10
As organisms decompose waste, they generate heat. Decompositionis most rapid when the temperature is between 90° and 140°F (32 - 60° C). Below 90° F (32° C), the process slowsconsiderably, while above 140° F (60° C) most microorganismscannot survive. Compost pile temperature depends on how the heatproduced by microorganisms is offset by the heat lost throughaeration or surface cooling. During periods of extremely coldweather, piles may need to be larger than usual to minimize surfaceheat loss. When composting high nitrogen wastes, like grass clippingsin the summer, smaller piles and frequent turning are needed toboth provide oxygen and release excess heat.
The above is a graph of typical compost temperatures. Afteran initial high temperature period (of a few days to several weeks),compost pile temperatures will gradually drop. Turning the compostrejuvenates the oxygen supply and exposes new surfaces to decomposition,causing temperatures to rise. If temperatures rise above 160°F (71° C), the compost can sterilize itself, killing off thebeneficial microorganisms. Extremely high temperatures can alsostart the chemical process of spontaneous combustion, which mightlead to the outbreak of a fire. Turning the compost when temperaturesexceed 140° F (60° C) can prevent both these potentialproblems.
When the temperature drops below 70° F (21° C), thecomposting process is nearly complete. However, it is also possiblethat imbalances of oxygen or moisture are causing the pile tocool. If the compost is properly moist, and turning does not causetemperatures to rise, the compost is probably finished.
Temperature monitoring is very important for managing the compostprocess. By measuring temperatures regularly, you can tell howfast material is composting, and whether there are hot or coldspots in the pile. Turning the compost whenever temperatures getabove or below the optimum range will help produce high qualitycompost in the shortest possible time.
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For specific comments related to this page, please contactthe Cornell Waste ManagementInstitute (format and style), or TomRichard (technical content).
This page was created on August 24, 1995
This page was last updated October 2000
