Many gardeners have used cover crops to help keep soil from blowing away over winter. An added benefit of raising cover crops is that the foliage and root growth can be tilled under in late winter to help loosen heavy soils and improve overall soil structure and fertility. Also known as “green manure,” these cover crops can be especially valuable in preparing a new site for gardening or for rehabilitating a heavy or compacted site.
Cover crops are generally sown in late summer or early fall. In established gardens, wait until after summer vegetables are harvested. The type of crop to grow will depend on the desired function, as well as availability. Winter rye, buckwheat, hairy vetch and winter wheat are ideal for use as cover crops and are among the most commonly available through garden centers and mail-order catalogs.
The amount of seed to plant will vary with the species, but, in general, winter cover crops are seeded at a rate of 2-3 pounds per 1,000 square feet. Till or spade the soil, and scatter the seed over the area to be covered at a depth corresponding to the size of the seed. Large seeds should be covered with one-fourth to one-half inch of soil or compost. Small seeds can be left on the surface and lightly raked. Apply a thin layer of loose straw to protect the area from wind and runoff from heavy rains.
Fertilizing is generally not necessary, especially for established garden beds. Some members of the Legume family of plants, most notably alfalfa and hairy vetch, actually facilitate the fixing of nitrogen in association with certain soil-borne bacteria. The bacteria colonize in nodules of the legume’s roots.
The root growth of the cover crops will help loosen heavy or otherwise compacted soils, and the addition of the dead foliage later in winter or spring will improve aeration, water-holding capacity and nutrient status. The cover crop should be plowed under several weeks prior to spring planting time to allow the vegetation a chance to break down a bit. For plants that have a large volume of top growth that tends to get tangled in the tiller tines, mow the tops first, then till under.