Brandon Hines incorporates winter rye and hairy vetch cover crops in spring at the Center for Environmental Farming Systems, Goldsboro, NC. (Photo courtesy of Jack Horan.)
If you have harvested everything from your vegetable garden and decided not to plant cool-season crops, then now is the time to start a cover crop, which just means planting something to cover up the dirt. Big-time farmers plant cover crops such as clover and rye, and backyard gardeners can reap the same benefits for their dormant gardens during the winter months with a cover crop.
The benefits are many, according to Suzanne O’Connell, a graduate student at N.C. State University who researches cover crops on organic vegetable farms. Growing a cold-weather cover crop reintroduces nutrients to the soil, improves soil quality, can control weeds, breaks the cycles or diseases or pests, attracts insect pollinators and decreases soil erosion for gardens on a slope. “It’s adding work in one sense, but you really are improving your soil and adding nutrients,” O’Connell said.
Leaving your spent vegetable garden’s soil bare through the winter lets rain and snow leach out nutrients such as nitrogen. That nutrient loss is on top of those lost in the summer to vegetables such as tomatoes, cucumbers, squash and corn.
With summer gardens spent, fall is an ideal time to plant a cover crop, since most cover crops require between two and four months to reach their desired stage. Prepare the soil as you would for any other crop, applying lime or fertilizer as needed by a soil test. Broadcast cover crop seeds by hand.
O’Connell recommends five cover crops for all regions of the Southeast. They are easy to germinate and easy to get rid of in the spring when the garden is to be replanted with vegetables.
Crimson and berseem clover (Trifolium incarnatum, T. alexandrinum) – Plant six to eight weeks before the first frost date. Clovers are part of the legume family, which can fix nitrogen in the soil and thus boost nitrogen for next spring’s garden. Mow one or two times when about half of the crop is flowering. Allow the residue to decompose for at least two weeks before planting vegetables.
Cereal/winter rye (Secale cereale) – Plant six to eight weeks before the first frost date. A cold-hardy crop, rye will grow well into the spring. Rye increases soil organic matter as it decomposes. Mow one to two times when at least 12 inches tall, or when half of the crop has immature seed heads. Allow residue to decompose for at least two weeks before planting vegetables.
Buckwheat (Fagopyrum esculentum) – Plant in the spring or fall during a two-month period of mild weather. Buckwheat establishes quickly, suppresses weeds and attracts pollinators. Mow one to two times when half the crop is in flower and before hard seeds have formed.
Soybean (Glycine max) – Plant in early to midsummer, between spring and fall crops. Mow before pods have formed or when pods are still green and have not matured. These legume family plants can fix nitrogen in the soil.
Oats (Avena sativa) – Plant eight to 10 weeks before the first frost date. Oats grow during the fall and die when cold weather rolls in. They form a surface mulch, increasing soil organic matter as they decay.
Maintenance for cover crops is minimal other than watering if a long dry spell occurs.
In late winter or early spring, gardeners can blend cover crops – “green manure” – into the soil. First, mow the crop and let it dry out for a week or two. Then work the crop into the soil with a garden tiller or by hand with a shovel or pitchfork. O’Connell said that gardeners can either mix in the entire cover crop or create 1- to 2-foot-wide planting strips, leaving the rest as surface mulches that will decompose over time and serve as walkways. Such strip tillage works well with grain-type cover crops like rye and oats.
Spreading leaves over the garden will increase the amount of soil organic matter and control weeds, but the garden doesn’t benefit from that process as much as it does with a cover crop. Instead, O’Connell recommended composting leaves with other yard and household waste, and then adding the compost to the garden as a soil builder and natural fertilizer.
Cover crops also provide an aesthetic benefit. They add color, texture and blooms to a vegetable garden so that it looks vibrant and productive throughout the year.
Where can I buy cover crops?
Cover crop seeds are available at many garden stores as well as online through seed companies. For a list of cover crop seed sources, visit Noth Carolina State University Cooperative Extension's list of cover crops.