It is a generally accepted fact that once soil temperatures drop below 45°F (7°C), biological activity slows to a crawl, and the soil and all its life forms hibernate through winter. By this logic, soil cannot be expected to change for the better during the winter months, and yet it does when given a little help. Here are five ways to use the winter season to improve the soil in your organic garden.
1. Wait to cultivate.
One of the reasons why soil feels so loose and friable toward season’s end is that it is impregnated with the summer’s "crop" of fungal hyphae and mycelium – microscropic threads that will slowly rot through winter, along with roots left behind by veggies and weeds. As far as nature is concerned, the table is set, and you would most definitely crash the party if you dug and turned the bed. So, unless you have a good reason for doing so, for example you want to prepare space now for an early spring salad garden, in fall it is better to mulch over vacant beds without cultivating them first. However, you have my permission to disturb soil as needed to dig out nasty perennial weeds.
2. Use winter mulch.
Leaves are free for the raking, and they do a great job of protecting soil from the ravages of winter. But many other mulch materials work just fine, including wood chips – an increasingly popular mulch material in gardens with soil that has already been improved for several seasons.
3. Grow winter cover crops.
Fortunately, many cold-hardy plants that make great winter cover crops did not get the memo that they were not supposed to grow in winter. Winter grains in particular are specialists at protecting the soil from erosion through winter, all the while developing huge root systems that increase soil organic matter content. When cut back to the ground in spring, hardy legume winter cover crops like hairy vetch or winter peas leave behind nodules of nitrogen, ready for use by the next crop.
4. Tolerate winter weeds.
Weeds that grow in summer tend to be large, aggressive plants that quickly take over any planting, but winter weeds are different. There is seldom a crop present for them to smother, and common weeds like henbit and chickweed often form green mats of foliage that protect the soil from erosion. In addition, dandelions, bittercress, and several other winter weeds drill deep into the soil with their long, slender taproots, which improves soil drainage. Winter weeds are used as natural winter cover crops in some Australian fruit orchards, and this method can work in vegetable gardens, too. To keep winter weeds from reseeding too heavily, simply hoe them down in early spring, rake up the greens, and compost them.
5. Compost under cover.
Garden beds that will sit vacant until spring can be heaped up with compost (without cultivating them first), and then covered with an old blanket or even a low row cover tunnel. In this way, the bed benefits from a deep layer of compost at the surface, which is further enhanced by a cloth cover. A cloth cover moderates how much moisture reaches the compost and soil below and cushions the bed, which reduces compaction caused by pounding rain.
Each year I find myself using this method more and more, because fall is the one time of year when I have enough compost on hand to be generous. In spring, I remove the cover, let the compost breathe for a day or two, and then dig it in. My soil loves it.