Effects of Temperature on Composting

We’ve previously discussed how successful composting requires the correct ratio of nitrogen to carbon materials, plus oxygen and moisture. Temperature is also an important part of the composting process.

Aerobic composting produces heat as a by-product. The multitude of microorganisms that feed on organic matter in a compost pile create heat as part of the decomposition process.

Due to moisture content and the heat generated by these microorganisms, you may even see steam rising from your compost.

Thank you to our friends at Cold Creek Compost for these incredible shots of steam rising from their Aerated Static Piles!

View of steam rising from compost piles at Cold Creek Compost

Depending on method, local climate, moisture levels, and pile size, compost can get pretty hot!

Large, specially managed compost piles (as part of a biomeiler, or compost heater) can even create high enough temperatures to heat water or supply radiant heat to buildings and greenhouses.

Compost hot tub anyone?

Why Does Compost Get Hot?

The microorganisms present in compost use organic materials for growth and reproduction. As they consume and digest the carbon rich materials they release heat, which then gradually warms up the compost pile. As temperatures rise, new microorganisms move in!

Aerobic composting goes through 3 phases where different microbes work at different temperatures.

Psychrophilic 28-55°F
Psychrophiles are organisms found at low temperatures. Psychrophilic microbes get the compost pile started, but as it heats up they are replaced by Mesophiles.

Mesophilic 50-115°F
Mesophiles are responsible for most of the decomposition in a home compost pile. They prefer moderate temperatures and are happiest at around 98°F

Thermophilic 115-160°F
Thermophiles thrive at high temperatures. Commonly known as “Hot Composting”, this temperature stage is the most efficient for producing compost quickly.

Aerial view of steam rising from compost piles at Cold Creek Compost

Effects of Temperature on Composting

Good temperature management can tell composters how fast material is composting, when compost is ready, and whether there are any problems in the pile.

Higher temperatures in a compost pile speed up the overall process and create high quality compost, the wrong temperature can slow the process or kill off beneficial microbes. Temperatures between 90-140°F are usually considered ideal. At temperatures of 130-135°F compost is hot enough to efficiently kill off most pathogens, fly larvae, and weed seeds.

A compost pile may not heat up if it is too wet, too dry, or the wrong size. It will also not heat up properly if it is lacking nitrogen, oxygen, or bacteria. Compost that is too cold may become smelly and take a much longer time to break down.

Temperatures that are too high (over 160°F) will begin to kill off beneficial microbes and the composting process will stop. Turning or aerating compost before it exceeds 140°F can prevent it from getting too hot.

Many things can affect temperature change. Higher moisture piles can heat up more than dryer piles. Larger compost piles retain heat more easily than smaller ones. Even the outside temperatures can influence microbial activity and determine how hot a compost pile will become.