Winter has arrived and the garden is dormant. Or is it? On the surface, annual plants have died and are decomposing. Hopefully, the decomposition is taking place in a compost pile to forestall any pest or disease transmission in the spring. Perennials have withered, or been cut, back and have concentrated their energy in their roots. They wait for spring’s warm days to leaf out and bloom.
A quick glance at my garden reveals mulch, mostly leaves with a little straw, and a few bare branches above the soil. But things are happening on the ground’s surface or deeper in the soil. Even when temperatures drop below freezing, soil is alive with microorganisms — protozoan species, nematodes, insects, arthropods, and the largest common soil dwellers, worms.
Of course, during winter everything in the soil slows down. Some of the less complicated organisms, like bacteria, can tolerate freezing. Bacteria membranes can stretch so they don’t burst when their internal fluids become ice. Soil that is rich in humus (that wonderful end product from the compost pile) is the perfect hibernation habitat for bacteria and other organisms. Humus provides a rich carbon habitat that shelters overwintering creatures so they can get a jump on soil activity in the spring.
While bacteria overwinter, soil fungi set spores. When spring temperatures rise or a warm spell heats up a string of days during the winter, they sprout. There are many harmful and beneficial soil fungi. One beneficial fungi, trichoderma, attacks destructive fungi in the soil and on plant surfaces. It prevents snow molds that can form on lawns underneath snow cover. Healthy winter soil is alive with fungal microorganisms and gives plants and seedlings a boost come spring.
Worms, the big workhorse dwellers in the soil, have their own strategy for surviving winter. Common earthworms burrow deep into the subsoil before the soil freezes. They’ll travel down, aerating and loosening soil as they go, as deep as six feet! Once below the freeze line, they form a slime-coated ball and hibernate in a state called estivation. As a mucus-wrapped bundle, they can survive the long months before the spring rains wake them from their hibernation.
Worms will survive above the freeze line too. They’ll congregate in a warm pocket of soil; say, against a concrete wall or under a rain barrel or a plastic bag of leaves. The thermal mass of the wall or barrel heats the soil, creating a micro-environment for the worms. In January, it’s fun to find a tiny Florida filled with a wriggling mass of worms. Occasionally, I disturb my compost pile in the winter. When I do, I always find common earth worms nestled as tight bundles inside uncrushed egg shell halves.
Not all worms hibernate. Some lay eggs in cocoons, ready to hatch when conditions are ideal. Once their eggs are laid, they freeze and die under the leaf litter or mulch. One Northern worm, S. niveus, has evolved to manufacture glycerol as “antifreeze” in their internal fluids. They supercool their bodies and can survive even the coldest winter weather.
How can you promote beneficial fungi, healthy bacteria growth and a happy, wriggling worm population? Consider planting a winter cover crop in the fall. Add compost to your soil. Mulch the soil to prevent moisture loss and reduce soil temperature fluctuations. Mulch also protects perennials from wind damage. Even though winter has fully arrived in Missoula, it’s not too late to mulch. Purchase a straw bale or two from any of the feed supply stores and spread a six to eight inch layer over your garden. In the spring, your soil will reward you with strong, healthy seedlings and plants!
This article originally appeared in the December 2013 issue of The Regular Joe.