CORVALLIS, Ore. — If your backyard compost pile is not getting hot, it can still make good compost.
A cool pile will break down yard trimmings and fruit and vegetable scraps over time. Microorganisms need air, moisture, temperatures above freezing and patience. A hot pile can finish in weeks. A cool pile can take three to six months or longer, but it requires far less management.
Adjust for your region
Cold composting works statewide, but moisture management is different across Oregon.
Western Oregon
- Rain usually keeps piles moist.
- Site the pile where excess water can drain.
- In very wet periods, cover loosely so the pile stays damp, not soggy.
Oregon Coast
- Protect the pile from constant rain and wind with a lid or anchored tarp.
- Keep ventilation so the pile does not turn anaerobic.
Central and Eastern Oregon
- Add water whenever you add material so the pile stays like a wrung-out sponge.
- Place the pile in light shade or behind a windbreak to reduce drying.
- Expect a longer breakdown time in cold, dry winters.
What you can skip
Slow composting is forgiving. You can skip several chores that hot composting requires.
- No precise carbon-to-nitrogen ratio. A woody pile will simply decompose more slowly.
- No commercial inoculant. Yard debris and kitchen scraps already contain the bacteria and fungi needed.
- No turning schedule. You can just pile material and let it sit.
Drawbacks and easy fixes
A cold pile does not get hot enough to kill most weed seeds, so keep problem weeds out of the pile. Plant diseases in leaves or soil on roots can also survive. Apply finished compost from a cool pile in a limited area first to be sure it does not spread problems.
Critters may explore a cool pile if it contains kitchen scraps. Consider these options instead:
- Compost scraps in a critter-proof container.
- Bury scraps in a well-drained part of the garden.
- Feed scraps to a worm-composting bin.
If you still add scraps to the main pile, bury them deep in the center of a large pile to deter animals.
Keep odors down
A pile made mostly of grass clippings can mat, shut out air and smell like ammonia. To prevent this:
- Break up and redistribute clumps to add air.
- Mix grass with drier material such as leaves.
- Leave grass clippings on the lawn to decompose in place.
Even if a cold pile takes longer, it keeps organic material out of the waste stream and gives you compost for the garden with very little work.
Previously titled Slow, cool composting is the easy way
