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Let winter cover crops improve next year's garden

By Bob Westerfield
University of Georgia

Fall is arriving at last. When the first frost wields the final blow to our summer vegetable bounty, many gardeners just let the plants die out and leave the soil exposed.

But there's a much better idea: Consider planting a winter cover crop.

Often called green manures, cover crops are an economical way to both protect and build the soil. Their nice green color looks pretty good, too, when most things are drab and brown.

Cover crops are usually a grass or legume such as clover, planted on the garden site to help hold and build the soil. You can use both summer and winter cover crops for either season. For now, though, let's focus on the winter type.

Growing cover crops offers many benefits:

  • Reduced erosion.

  • Improved soil structure and reduced surface crusting.

  • Increased water-holding capacity of the soil.

  • Reduced winter weed growth.

  • Reduced herbicide injury.

  • Winter hardpan penetration, improving the soil for the crop that follows.

  • Added nitrogen if the cover crop is a legume.

Types

There are two general types of cover crops, leguminous and nonleguminous. Leguminous cover crops, such as vetch and clover, add nitrogen to the soil. Nonleguminous ones, such as wheat and rye, don't fix nitrogen but are preferred on erosive soils.

Crimson clover is probably the most commonly used and most desirable of the clovers grown for a cover crop. It matures earlier and produces more nitrogen and dry matter earlier than most other clovers.

An excellent crop of crimson clover can produce up to 120 pounds of nitrogen per acre, and 30 to 50 pounds is common.

Nonleguminous cover crops (rye, ryegrass and wheat) have several advantages. For one thing, they cost less to get established than a leguminous crop. They provide longer and better erosion control, too, because they grow more in the winter and have fibrous root systems.

Their major disadvantage is that they don't fix nitrogen and usually require some nitrogen fertilizer when you plant them.

Plant early

It's important to plant cover crops early to establish early root growth before cold weather comes. This helps the crop better survive a hard winter. Plant legumes in mid-September to mid-October and grasses in early October to mid-November.

A soil test from your county University of Georgia Cooperative Extension agent will tell you how much lime, phosphate and potash your cover crop needs. If your soil needs lime, phosphate or potash, apply them in the fall just before preparing the seedbed.

If you're growing a legume cover crop, don't add a heavy nitrogen fertilizer. However, treat the seed with the correct nitrogen-fixing bacteria. This inoculant is important to ensure good germination.

Prepare the seedbed the same way you did for your spring garden. Either remove or till in old crops, working the soil while it is slightly moist but not wet.

Raked or drag in the seeds of grass-type cover crops to a depth of one-half inch. Clover-type seeds are tiny. Only lightly rake them in to provide good soil contact (don't bury the seed).

Improving the soil with cover crops is a long-term venture. Over time, these crops can and will add organic content to the soil. When spring arrives again each year, just till them in to help feed the next year's vegetable garden.

(Bob Westerfield is the Cooperative Extension consumer horticulturist with the University of Georgia College of Agricultural and Environmental Sciences.)

(Bob Westerfield is a Cooperative Extension horticulturist with the University of Georgia College of Agricultural and Environmental Sciences.)

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