By Elaine Applebaum, UC Master Gardener of Placer County

Q: I’ve heard people talk about growing a “cover crop” but don’t understand what they mean. Can you explain? 

A: Unlike crops that we grow to eat, cover crops are grown to feed the soil, protecting and improving it for future plantings. It is an old practice that has gained new interest as farmers and backyard growers seek ways to reduce the amount of chemical pesticides and fertilizers they use.

Sometimes called “green manure,” cover crops are a way to produce organic material to incorporate into the soil. The crop is grown, then turned under. This enhances soil structure, provides aeration and improves water retention and drainage. Earthworm and microbial activity increases and nutrients needed for healthy plant growth are recycled as the organic material decomposes. Cover crops also provide habitat for natural predators, the “good bugs” that control aphids, thrips, and other pests.

Cover crops can be used any time of the year, but are probably most commonly planted by backyard gardeners in the fall, after final harvest of summer vegetable crops. The cover crop grows over the winter, watered naturally by our seasonal rains. As an added bonus, it prevents erosion and reduces weed growth that may otherwise occur on bare soil. In early spring, when the crop begins to flower, mow it down and immediately mix it into the soil. Given enough time at the right temperature, the material will decompose in time to plant your summer vegetable or flower garden. You can speed up the breakdown by turning the soil every couple of weeks until planting time.

What plants are used for cover cropping? Legumes, such as, peas, beans (bell and fava), vetches, clovers, and alfalfa, are all good choices because they are able to pull nitrogen from the atmosphere and convert it to a form useable by your plants. Mustards (Brassica spp.) have deep roots to help break up compacted soils and bring minerals and nutrients closer to the surface. Grains and grasses such as barley, oats, wheat, and rye are good sources of organic material. Many gardeners plant a mixture of several of the crops listed. Seeds can be found at farm supply stores and larger nurseries.