Ten things to remember about composting during the winter

Healthy organisms in a balanced compost will be active, hot, and produce steam even in the winter.

For decorative purposes.
Steaming compost pile on a cold day. Photo by via CC BY-SA.

Wintertime concerns about compost piles and bins are common. Looking at our compost bins and seeing them covered in ice and snow make us begin to think that the pile is frozen and has stopped working. And in some cases, is has slowed considerably but I assure you the organisms are just waiting to warm up a bit. Compost piles that are actively managed will continue to decompose all winter long–just a bit more slowly. The active bacterial colonies change with the temperatures of the compost. Hot piles promote thermophilic organisms (those that like heat). Ambient piles are mesophilic bacteria are at work and are the most common organism present; and psychrophilic bacteria are organisms that are active in the cold. They work just as hard, just a bit slower than the others.

Sometimes the opposite is true. A very active pile is steaming away and a neighbor or friend may think that the compost is spontaneously combusting! Steam is a healthy by-product of a bioactive compost pile and not a fire. Here are ten important things to remember about your compost during the winter:

  1. Many organisms continue to thrive under the snow in winter.
  2. Hot composting typically averages temperatures around 150 to 175 degrees Fahrenheit for a short time and requires a minimum size of 3 feet x 3 feet x 3 feet (5 feet is best) before cooling to ambient temperatures due to limiting factors. This method of composting requires more than just leaves to effectively work such as the addition of grass clippings and other nitrogen rich materials.
  3. Spontaneous combustion of home compost piles is rare and usually is associated with other contributing conditions, such as composting indoors and an imbalance of carbon to nitrogen ratios.
  4. Compost temperatures must reach 300 F to 400 F (150 to 200 degrees Celsius) for spontaneous combustion of materials to take place. This is unlikely to happen outdoors during a Michigan winter.
  5. Do not confuse steam from your compost in the cooler months with fire. Compost piles will steam, and actively managed piles often have the snow completely melted off throughout the winter.
  6. Covering your winter compost pile with straw or leaves can help insulate its core to keep it warmer longer.
  7. Cold composting and sheet composting or sheet mulching is acceptable for leaves and reduces temperature of the pile if you do not plan to actively manage your compost. Just know that this is a cold composting method and takes much longer for the material to decompose.
  8. Avoid adding invasive plants and/or seeds to your compost piles in the fall and winter. Due to lower decomposition temperatures these plants may not be destroyed and will find your compost a great place to “overwinter.” Hot composting temperatures are needed to destroy most pathogens and weed seeds.
  9. Do not compost near a body of water or shore of a lake or stream. Compost can contribute unwanted nutrients to the water.
  10. Composting is the best alternative to managing backyard waste and kitchen food scraps. It reduces the amount of waste you produce and supplies a beneficial soil amendment product.

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