Cover crops usually are grown to prevent soil loss from wind and water erosion. Use fast-growing cover crops, such as winter wheat or annual rye, on fall-spaded gardens. A second, and probably more important reason home gardeners should use cover crops is to improve soil structure and increase organic matter. This is accomplished by tilling cover crops into the garden while they're green and growing. This technique, which is referred to as green manuring, speeds up the natural soil-building process and can reduce weeds. It also improves conditions for beneficial soil microorganisms and earthworms, and increases the soil's ability to hold water.
Common cover crops include annual ryegrass, Sudan grass, oats, buckwheat and legumes, such as peas, beans, alfalfa, clover and vetch. Leguminous plants are able to host bacteria that take nitrogen from the air and fix it in nodules on root hairs. To assure that the right bacteria are in the soil, inoculate legume seed during planting. Garden centers and nurseries carry the products you'll need to do this.
You can sow cover crop seeds in the fall and turn them under in the spring. You also can plant them in different sections of the home garden early in the spring. This can be done over several growing seasons. This rotation will improve a large vegetable garden over several years. For example, a home gardener with limited space can select out a section and produce food, and at the same time improve the soil. First, plant peas, and harvest them as early as possible, then turn under the vines. Next, plant snap beans or another legume, harvest and till under again. Finally, plant annual ryegrass as early in the fall as possible. It may die over the winter, but it can be tilled under in time for the new growing season.
Fill bare spots in your garden with a cover crop, but be sure to turn under the cover crop before it goes to seed. Like all plants, cover crops become weeds when they grow where they're not wanted.
For more information, see the following Colorado State Extension fact sheet(s).
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Updated Tuesday, October 13, 2015