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Cover crops, also known as green manures, are an excellent tool for vegetable gardeners, e spe c ia l ly where manures and compost are unavailable. They reduce soil erosion during the winter, add organic material when turned under in the spring, improve soil quality and add valuable nutrients.
Popular fall-planted cover crops include oats, winter rye, winter wheat, daikon radish (also called “tillage radish”), crimson clover and hairy vetch. The latter two crops are legumes ‒ plants that can add a lot of nitrogen to your soil after they decompose. These crops are typically planted as early as Aug. 15, but no later than Oct. 10. They should make some growth before the first hard frost. Some cover crops (oats and daikon radish) are killed by cold winter temperatures, but most go dormant and resume growth in the spring. Other cover crops, like buckwheat and Dutch white clover, are sown in the spring or summer to cover and improve bare soil.
Cover crop roots grow deeply into the soil pulling up nutrients that might otherwise leach out of the soil. Winter garden covers are turned into the soil, usually in April, because they grow vigorously and will go to seed in May.
Seeding rates for winter cereals are generally 3 to 4 ounces (by weight) per one hundred square feet; 1 to 2 ounces for crimson clover and daikon radish. Combine legumes and non-legumes when possible. If you plant a two-species mixture, use about 60 percent of the recommended amount for each. Oats can be a good choice if this is your first time trying a cover crop or if you want to be able to plant early spring vegetables. Oats are killed after a couple of heavy frosts or freezes, leaving a brown decomposing mat in spring. Daikon radish if planted now can put down a tremendous edible root. A gardener can pull some to eat well into the winter and leave others to rot in the soil to feed soil microbes and improve soil tilth.
Not all garden supply centers sell seed by the pound. Rockbridge Farmers Cooperative does sell most of the seed species mentioned in this column by the pound. You can also mail order cover crop seeds from a retail seed company.
Spring planting may be delayed somewhat by a cover crop since you must allow at least two weeks for the plants to break down and the top six inches of the soil may need to be turned and worked more than once.
Most of the content of this column comes from an excellent article by Jon Traunfeld with the University of Maryland Extension Service. For a complete copy of this article, call Tom Stanley at the Rockbridge Extension office. The online version of the article also features some helpful videos on cover crop management. For an electronic link to the article, send email to stanleyt@ vt.edu.
