The cold temperatures of winter fundamentally change composting from an active, heat-generating breakdown to a state of slow processing or near-total dormancy. When the internal temperature of the pile drops, the rapid decomposition driven by heat-loving, or thermophilic, microorganisms slows dramatically. The goal shifts from producing finished compost quickly to protecting the existing material and storing new organic additions effectively. During this seasonal transition, the compost pile functions as a holding bin, preserving materials until warmer spring temperatures allow microbial communities to become active once more.
Adjusting Input Materials
The routine of adding daily kitchen waste continues through the winter, but the method of incorporation must change. Instead of small, daily additions, add new material in larger layers or batches whenever possible. This minimizes the frequency of opening the pile, reducing heat loss and exposure to cold air. New material should be completely buried inside the pile to retain warmth and begin breaking down.
A common issue in winter is the lack of available dry “brown” material, such as leaves or shredded paper, needed to balance nitrogen-rich kitchen “greens.” Stockpile a significant volume of shredded leaves, straw, or sawdust in the fall for use as a covering layer over new kitchen scraps. Favoring dry, carbon-rich material helps absorb excess moisture from food waste, preventing the pile from becoming a wet, anaerobic mass when the spring thaw arrives.
If you produce a large volume of kitchen scraps daily, or if the pile is completely frozen, store the “greens” until spring. Food waste can be collected in bags or buckets and kept in a cold garage or freezer. Freezing the material has the added benefit of rupturing cell walls, which speeds up decomposition once the material is added to the pile in warmer weather.
Protecting the Pile Environment
Protecting the physical structure of the compost pile from external cold and moisture is necessary. The primary objective is to insulate the existing volume to retain residual heat and prevent deep freezing. Surround the sides of the compost bin with dense insulating materials, such as straw bales, thick layers of loose straw, or old carpet pieces, to create a thermal barrier against the cold air.
The top of the pile is vulnerable to saturation from heavy snow and winter rain, which introduces excessive moisture. A wet pile loses heat quickly and can become anaerobic, leading to foul odors upon thawing. Cover the top of the pile with a fitted tarp, a sheet of plywood, or a thick layer of dry straw or cardboard to deflect precipitation. This covering should still allow some air exchange, but its main function is keeping internal moisture levels balanced.
Managing Internal Activity and Aeration
During sustained freezing temperatures, biological processes within the compost pile slow significantly, making the physical effort of turning the pile unnecessary. The active thermophilic bacteria become dormant, and any breakdown is handled by cold-tolerant psychrophilic organisms at a much slower rate. Therefore, the frequent turning and mixing required for active composting in warmer months can be discontinued.
Turning a cold or frozen pile is counterproductive because it releases residual heat from the core, driving the temperature down and slowing the process further. If the pile is frozen solid, attempting to turn it risks damaging tools or the bin structure. In most cold climates, the compost material is best left undisturbed until the spring thaw.
The material added over the winter is essentially kept “on hold,” waiting for the return of warmer weather. Once ambient temperatures rise, microbial activity will rapidly resume, and the decomposition of the stored materials will accelerate. A well-maintained winter pile provides a significant head start on producing finished compost for the spring planting season without constant maintenance during the cold months.