Hartley Magazine

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It’s high composting time in Chicago

The trees are abandoning their leaves, the perennials are giving up on their leaves and stems and I’m dumping out my pots of annuals. And all the abandoned plant debris from the yard, garden or greenhouse ends up in the compost.

I’m amazed every March to find a bounty of compost in bins that started out empty in October and filled up with leaves and dead plants and odd and ends by Thanksgiving. I understand how it happens: through the fine dining of bacteria and fungi, pill bugs and earthworms, all the happy organisms that make their living digesting my compost. But I still marvel that it can happen in the dead of a Chicago winter.

By November, it’s cold enough that a few hours of planting bulbs will leave me red-nosed and stiff-fingered. How can bacteria stay alive in a frigid pile of leaves and dead begonias?

Well, it’s partly the leaves and dead begonias. They trap air for insulation, like layers of quilts or a well-insulated greenhouse. A layer of snow insulates too. The cold may penetrate a few inches—and a few inches more, as it gets colder—but the organisms simply retreat toward the center. Rarely does a good-sized pile freeze all the way through.

The bacteria also help themselves. They turn the food they consume into energy and give off that energy as heat. That’s why you can sometimes turn over a large, moist pile and find it literally smoking from the heat given off by a bacteria population boom. In the winter, the cold keeps populations down. But as long as there are some bacteria consuming something in the middle of the pile, they still will warm it up a little for all the insects, arachnids, nemotodes, earthworms and other inhabitants.

The larger the pile, the larger the unfrozen zone in the center. My three compost bins are of various designs and materials but are all about three feet across, pretty much the minimum size that can get through most winters without freezing solid.

The bins are another buffer: A container breaks the wind and holds in moisture better than a naked pile. The critters need moisture to survive, digest, reproduce and throw off heat. And if the outer regions have water to freeze it actually protects the center. The drying wind can’t blow through ice.

One of my bins has a lid for added protections, and there I can expect that nearly everything will be digested into compost by spring. In the uncovered bins, there’s less protection and less activity. If I remember to mulch them well with leaves, though, they will stay warmer and break down more completely.

So as I move around my garden, raking, cutting back, clearing up and collecting, I know that every load of debris I dump in the compost is an investment. The larger the pile, the more critters can stay busy through the cold months. I can dump the remains of my favorite containers and the remains of my worst mistakes, and the bacteria don’t care. They’ll take it all and pay me back with good, rich compost next spring.