Composting slows in winter, and across most of Canada a backyard pile will partly or fully freeze for weeks at a time. That is normal. The microbes responsible for decomposition become inactive in the cold rather than dying off, and the process resumes as the pile thaws. The aim through winter is less about fast finished compost and more about keeping material contained and ready to restart in spring.
Why the pile slows down
Decomposition is driven by microbial activity, and that activity falls sharply as temperatures drop. A large, well-insulated pile can hold internal warmth longer than a small one, but once deep cold sets in, even a big pile cools to ambient temperature. A frozen pile is paused, not ruined.
Keep some activity through winter
Building volume before the first hard frost helps, since a larger mass loses heat more slowly. Insulating the sides with stockpiled leaves or straw and locating the bin in a sheltered, sunnier spot can extend activity into the cold months. Chopping kitchen scraps small gives microbes a head start during any thaw.
Managing scraps when the pile is frozen
Kitchen greens keep arriving even when the outdoor pile is solid. A few approaches keep them out of the garbage:
- Collect scraps in a sealed indoor container and add them during thaws or in spring.
- Keep a generous reserve of dry browns nearby so frozen, wet greens can be balanced as they are added.
- Where a municipal green-bin service operates through winter, route excess kitchen organics there.
Reading common problems
Most complaints fall into a few recognisable patterns. The table summarises what each one usually points to.
| Symptom | Likely cause | What helps |
|---|---|---|
| Sour or rotten smell | Too wet, too many greens, low airflow | Add browns, turn to aerate |
| Ammonia smell | Excess nitrogen from greens | Mix in carbon-rich browns |
| Pile will not heat in mild weather | Too dry, too small, or too many browns | Add greens and moisture, build volume |
| Animals disturbing the pile | Food scraps that attract wildlife | Remove meat and dairy, use a closed bin |
| Fruit flies near the surface | Exposed fresh scraps | Bury scraps under a layer of browns |
Restarting in spring
As the pile thaws, turning it reintroduces air and mixes the winter additions into the warmer core. Activity usually returns on its own once temperatures rise; adding fresh greens and a little moisture at that point helps the pile regain momentum. For general guidance that applies across regions, municipal composting pages and the Environment and Climate Change Canada resources are publicly available starting points.