The use of cover crops reduces erosion and maintains and builds nutrients for your garden over the winter.
Turning under vegetation in the fall allows earlier planting in the spring and is especially good for heavy soils, since they are exposed to the freezing and thawing that takes place during the winter. This helps to improve soil structure. A cover crop's roots hold the soil, decreasing erosion during the winter. Tilling under the cover crop in the spring adds organic material to the soil, improving its structure and porosity and adding valuable nutrients. Winter cover crops can be planted from September 1 through November 1 (optimum planting is September 1 to October 15). Where you have fall crops growing, you can sow cover crop seed between rows a month or less before expected harvest. This way the cover crop gets a good start but will not interfere with vegetable plant growth.
Some cover crops suitable for winter use are legumes such as crimson clover, fava beans, or hairy vetch. Non-legume cover crops such as barley, winter rye, or winter wheat may also be used with good results. Mixtures of legumes and non-legumes are effective as well. Ask at the seed store or your local Extension office what the best type of cover crop for your area is, and at what rate (pounds per 100 square feet) to plant it.
Prepare the soil for cover crop seed by tilling under plant wastes from the summer. Broadcast the seed, preferably before a rain, and rake it evenly into the soil. Spring planting may be delayed somewhat by the practice of cover cropping, since time must be allowed for the green manure cover crop to break down. If you have crops that need to be planted very early, you may prefer to cover a section of the garden with mulch.
Some gardeners are experimenting with various types of conservation-tillage gardening to reduce weed problems and prevent erosion and moisture loss. The standard no-till practice used on farms involves sowing a fall cover crop, killing it in the spring with an herbicide, such as paraquat, and planting vegetables in the dead sod (after a recommended waiting period). However, there are no emergent weed herbicides recommended for use in established home vegetable gardens at the present time. Use of weed-killers normally recommended for lawns or other areas is not advised, and until a safe herbicide is available for emergent weeds, this type of no-till practice is unsafe for growing vegetables in the home garden.
Another alternative is the use of a living sod, mowed regularly, which has many of the benefits of no-till and does not necessitate the use of herbicides. This practice works best with raised beds, so that only the paths need to be mowed.
Dr. John Luna at Virginia Tech reports success using a combination of winter rye and hairy vetch as a fall-sown cover crop, harvesting it with a scythe in the spring, planting through the stubble, then using the top material as a mulch as the season progresses. Also, this option does not require herbicides.
The use of cover crops over several seasons or years in a particularly weedy section of the garden is particularly useful in reducing weed problems and water demand.