Improving Garden Soil Over the Winter



There are two main ways to approach winter soil improvement: the mulch method and the cover crop method.

Improving Your Garden Soil Over the Winter

You may not think of winter as a prime time to garden, but actually there is a great deal that you can do during the winter months to ensure a bountiful harvest during the next growing season.

So what can you do now to get your garden off to a good start next year? There are two main ways to approach winter soil improvement:

  • The mulch method.
  • The cover crop method.

The Mulch Method

The simplest way to improve soil over the winter is simply to cover it with a thick layer of organic material. This mulch will protect the soil from the elements, and it will break down and contribute nutrients.

You can use any organic mulch material for this purpose. Straw is a reliable choice, and it is very inexpensive in some areas. For the fastest soil improvement results, however, fallen leaves are hard to beat due to their high mineral content and rapid decomposition. However, they should be covered with another material to keep them from blowing away. Also, avoid black walnut leaves and leaves that have fallen into yards with pets.

To prepare your garden for winter using the mulch method, take the following steps after a killing frost:

  1. Clear away all garden plant residue to avoid pest and disease buildup.
  2. Spread about half an inch of compost across the surface of the entire bed or plot. (This adds more nutrients and allows the compost to cure over the winter, particularly beneficial if you use the hot composting method.)
  3. Cover the bed or plot with six inches of leaves.
  4. Spread six inches of straw on top of the leaves.

In the spring, you will want to pull aside this thick mulch a day or two before you are ready to plant to give the soil a chance to warm up in the sun. Either pile it up in an unused corner of the plot to use as mulch as your seedlings grow or add it to the compost pile to get it out of the way.

The Cover Crop Method

Cover-cropping builds soil even faster than mulching, but it does require advanced planning. Most winter cover crops are planted in late summer to early fall, allowed to grow during the winter, and terminated sometime in the spring. The precise timing for each step will depend on what cover crop you choose.

A cover crop combination that works for many vegetable gardeners is winter rye and hairy vetch. The rye develops a thick stand that suppresses weeds and builds organic matter levels dramatically, while the hairy vetch is a legume that fixes nitrogen and appears to develop soil particularly suited to tomato growth.

Planting a cover crop is easy:

  1. Clear away all plant residue and mulch.
  2. Gently rake the soil to prepare a smooth seedbed, breaking up clumps and clods as you work.
  3. Scatter the cover crop seed over the surface of the soil by hand, aiming for an even and generous distribution.
  4. Lightly rake the soil again, just barely covering the seed.
  5. Gently pat the soil down with the back of the rake to ensure good seed-to-soil contact for better germination.
  6. Water the soil thoroughly. Keep the surface moist at all times until the cover crop has germinated.

You may need to water the cover crop from time to time until it is established, but once the seedlings have taken hold and begin vigorous growth you can walk away and let it do the rest of the work until spring.

When spring returns, you will want to give the cover crop a little time to grow and build biomass prior to planting your vegetables. However, never allow the cover crop to go to seed, as it will then become a new type of weed that you will spend the summer battling. You want to cut the cover crop down while it is still green, tender, and rapidly growing.

When you are almost ready to plant, you can simply till the cover crop in, assuming that you till your garden. If you are a no-dig gardener, however, you will need to chop it down instead. Small plots and beds can be tackled with a hoe. Larger plots are candidates for mowing or scything.

Because too much organic matter on the surface of the soil hinders seed germination, and because some cover crops (such as winter rye) produce compounds that limit the growth of other plants, give the cover crop about 3 to 4 weeks to decompose before planting your vegetables. No mulch will be required during this time period because the large quantities of organic matter from the cover crop will serve as an extremely effective mulch.

Whichever method you use to build your soil over the winter, the mulch method or the cover crop method, these two simple ways of preparing your garden for a new year will yield tremendous benefits in soil nutrients and organic matter levels.

Helpful Resource

Soil Quick Start
More tips and resources for building healthy soil, including a step-by-step guide to soil improvement.

Improving Your Garden Soil