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Good compost will be active, cook through winter

Ever wonder what happens in your compost pile over the winter? While almost everything else in the garden is either dormant or flat out dead, the compost pile is still alive and cooking.

Compost piles work because the right ratio of brown and green materials allows bacteria and fungi to begin breaking the material down. Generally, the ratio of materials should be about two parts brown or high carbon garden waste to one part green or high nitrogen stuff. Any nonwoody brown-colored garden waste is the carbon source while fresh, green materials are the nitrogen source. You can continue building your pile through the winter but the materials on the outside surface won’t be attacked by the microbes until next spring. The materials will, however, be broken down by freezing, creating more surface area for the microbes to work on when it warms up. All the real winter activity is deep in the pile.

Your pile needs to be at least three square feet so that the center of the pile has enough mass to work properly. The outer layers of the pile will act as an insulation blanket that allows the microbes, fungi, insects and earthworms to continue working albeit more slowly inside the pile. If we get a long stretch of weather below 20 degrees, however, a pile may freeze and stop activity until it thaws.

One major partner in the composting process and the garden in general is the earthworm. Two million of these humble creatures in a 2-acre area can move up to three million pounds of earth each – for free. There are at least 30 different types of earthworms in North America.

So just where do the worms go when a pile or garden gets cold? In general, they sense the cold and move deeper into the soil. Night crawlers, one of the largest worms, will move 6 feet down and enter a reduced metabolic state known as estivation. They curl up in a tight ball and cover themselves with a slimy layer to prevent dehydration and wait for spring. Other worms will move to varying depths. Those that don’t will freeze and die, leaving egg capsules that will and hatch in the spring. Once it warms up, the worms return to the shallow soil depths and resume their activities.

Because earthworms are such an important part of garden health, gardeners need to care for them like any other garden activity. One of the simplest ways to do this is to add organic material to feed them and reduce how often you rototill the soil. Rototiller tines destroy worm tunnels as they turn the soil, and chop up worms. Therefore, rototill in late March before many of the worms return to the upper soil layers and in early November after they have gone deep in the soil. Research shows that worm populations increase even more when tilling is reduced to every other year or not at all.

Pat Munts is a Master Gardener who has gardened the same acre in Spokane Valley for 30 years. She can be reached by email at

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