Ask A Master Gardener – Cover Crops in the Home Garden

Each year that vegetables are grown in a garden, nutrients are consumed from the soil. Eventually the nutrients will be depleted unless something is done to replenish them. One method of replenishment is to plant a cover crop.   What is a cover crop, why should home gardeners consider them, and which ones are best for home use?  Cover crops have been used by farmers for years to improve soil with minor investments in effort and time.

Most cover crops or green manure crops fall into two categories: grasses and grains such as rye, wheat, and oats; or legumes like clover, peas, and vetch. Cover crops are planted, allowed to grow for a period of time, and then tilled back into the soil.  This process returns nutrients to the soil, making them available to the next vegetable crop.  Tilling the cover crop back into the soil also increases the organic matter which in turn improves the soil structure and water-holding ability, and reduces soil erosion.  Since the cover crop is planted during the time when the vegetable crop is absent, it will suppress weed growth and disrupt soil-borne disease cycles.  It will also provide habitat for beneficial insects, a plus in any garden.

Cover crops are easy to plant and require only basic care to thrive. The key is to allow adequate time for the crop to grow, cut it before it flowers to prevent self-seeding and taking up the very nutrients that need to be replenished in the soil, and allowing adequate time for it to decompose before planting the intended crop.

Different crops provided different amount of plant material (biomass) and meet different needs. Some, such as legumes, will fix nitrogen in the soil. Warm season crops like buckwheat and clover can be planted in in the spring or summer in a fallow area or in place of vegetables for a portion of the garden (a set-aside section).  They will grow quickly and can be turned under in time for some late season crops to be planted.

Cool season cover crops, like oats, annual rye grass, and winter wheat, are planted in late summer and early fall. Realistically, mid-September is the cut-off for planting in central Wisconsin.  Those that are winter-killed (oats) are a good choice for gardeners who want to immediately plant the garden in the spring.  Those that resume growth in the spring (winter wheat) are good choices for areas that will be planted in warm weather crops like tomatoes, peppers, squash, and melons.

The procedure for planting cover crops is easy. Clear any garden debris and lightly till (or rake) to ensure good soil-seed contact.  Broadcast the seed by hand (rates can be found in the following UW publication: http://hort.uwex.edu/files/2014/10/Using-Cover-Crops-and-Green-Manures-in-the-Home-Vegetable-Garden-May-14-2014.pdf ) or by calling the UW-Extension Office. Rake the soil again to cover the seed to a depth of one-fourth to one inch depending on the seed size.  Water lightly, but do not create a crust on the surface.

In the spring, mow or use a string trimmer to cut the top growth of the cover crop. Wait a few days until the top dries, then turn under the crop.  In the case of winter-killed crops, tilling can be done as soon as the soil can be worked.  Wait 2-3 weeks for planting to allow time for decomposition to take place.

Carol Shirk

Certified Master Gardener

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