To an outsider's eyes, winter is a time when nothing happens in the garden. While it's true that gardens in most of the country are bedded down during the cold months, gardeners are seldom idle. Winter is when diligent gardeners maintain their tools, select seeds and prepare their potting areas for the coming spring. Composting doesn't stop in the winter, either, though it requires some preparation and extra work.
Compost in Freezing Temperatures
Composting depends on the activity of a complex ecosystem of bacteria and fungi that work together to break down the organic materials in your pile. Like other bacteria, they're most active at higher temperatures. Even in subtropical climates, researchers have found that winter slows the rate of decomposition (see References 1). In colder climates, where there's a risk of the pile freezing throughout, decomposition may stop until the pile thaws in spring. Wisconsin's Department of Natural Resources estimates that your pile needs to be at least 64 cubic feet in size to not freeze (see References 2).
As long as your compost is kept above freezing, it continues to work slowly through the winter. Municipal nonprofit organization Green Calgary in Alberta, Canada, where winter temperatures can drop to -40 degrees Fahrenheit, recommends protecting your compost as much as possible from the elements (see References 3). Build a windbreak around your pile using hay bales, bags of leaves or tarpaulins. Collect as many leaves as you can in the fall. Not only are they excellent insulation for your pile, but you can mix them with your kitchen scraps through the winter as a carbon source to balance the scraps' nitrogen.
Layering Winter Compost
It's still possible to compost in the winter, even if your pile is completely frozen. Keep carbon ingredients such as straw or autumn leaves near your composter, and layer them with your kitchen scraps. In the spring, when the pile thaws, the layered organic matter will break down quickly. If your pile is large enough to remain active and unfrozen through the winter, follow the same process. Chop your kitchen scraps into very small pieces to help speed decomposition, since the bacteria in your compost don't work as quickly in the cold weather (see References 3).
Another approach to winter composting is vermicomposting, or composting using worms. This style of composting uses an enclosed indoor bin, such as the inexpensive plastic totes available at many retailers. Fill the bin with topsoil, peat moss, straw, shredded newspapers and similar bedding materials. Purchase a pound of redworms from a bait shop or garden supplies shop, and add them to the bin (see References 4). According to the Environmental Protection Agency, a pound of redworms can process a half-pound of finely chopped kitchen scraps each day (see References 5). After three or four months, the finished compost can be used on your garden.
- Environmental Pollution; Composting of Spent Pig Litter at Different Seasonal Temperatures in Subtropical Climate
- Wisconsin Department of Natural Resources: Home Composting -- The Complete Composter
- Green Calgary: Winter Composting
- Oregon Metro: Composting With a Worm Bin
- U.S. Environmental Protection Agency: Vermicomposting