It protects the soil from being eroded by harsh winter winds and rains.
It helps reduce or prevent weed growth.
When turned under in the spring, the decomposition of the plants adds organic matter to your soil.
The organic matter improves soil structure.
It provides ideal conditions for earthworms and other soil organisms to thrive.
Roots from cover crops increase soil aeration and water infiltration.
Cover crops return minerals and nutrients to the soil.
When should you plant your cover crop? One way to determine this is when your annual garden plants (vegetables, flowers and herbs) are finished producing good quality and quantity of fruit. It may also be when you are tired of gardening and/or your schedule permits. Remove all plastic mulches, plant cages and stakes. Remove plants and add them to your compost pile (no weed plants that have gone to seed; chop plant debris into small pieces before adding to your compost pile). Rotary till the garden and prepare the soil surface for seeding.
Which crop should I choose for a cover crop? Barley, oats, wheat or rye are small cereal grains that are used for cover crops. They are known as non legumes. Winter varieties are planted in the autumn (between September and November) and make a great cover crop during the winter. They grow well on soil with fairly good drainage and a pH between 7 and 8. The seeds for any of these crops are available at most gardening supply stores. When planted in the early fall, they have an excellent chance to germinate and grow several inches. During the winter they will grow very little. With the arrival of warmer days in late February and early March, they will again begin to grow several more inches; just in time to be turned under as a green manure crop and to add rich organic matter to your garden soil.
Crimson clover, an annual legume, is also used as a cover crop. It is planted in the fall and grows quickly in the spring with warmer weather. It decomposes when turned under adding organic matter to the soil for warm season crops (tomatoes, peppers, sweet corn, melons, squash and lima beans) to use. It should be sowed mid-August to mid-September.
Legumes, like cereal grains when turned under in the spring, add organic matter to your soil, but they also increase the amount of nitrogen in your soil. How is this done? When seeds germinate and start to grow, the Rhizobia bacteria enter the developing root hairs, taking nitrogen from the air and fixing it in the nodules on the root hairs that plants then use. Plants need the right bacteria in the soil to make or fix nitrogen. To ensure that the bacteria inoculants are in your garden soil, it may be best to purchase the inoculants when you buy your legume seeds. Place seeds and inoculants in a bag and shake well, coating your seeds.
How do I plant my cover crops? Once plant debri is composted and the garden soil is tilled, then take a soil sample. Your garden should have a smooth seed bed for planting. After selecting the cover crop that is best for you, broadcast your cover crop seeds by hand. You may be able to use an adjustable lawn seeder by selecting the correct size for the seed. Gently rake the seed and soil surface making sure you have good soil and seed contact. If the weather conditions are dry and hot, irrigate the seed bed. If dry weather continues, keep the seeds moist while they are germinating and continue to water them as they grow into young plants.
When should I turn my cover crop under in the spring? Research studies show that your cover crop should be turned under around the beginning of April. However, if you are going to put in some early cool season crops (potatoes, onions, lettuces, etc.), you may want to just turn under enough to plant these crops. If turned under at this time, the cover crop will give the underground residue time to break down. When you turn cover crops under in the spring, it is called green manure. Green manure provides nutrients to the new crops that will be growing.
How do I turn under my cover crop? You can use a shovel to turn under the cover crop (mow first). This method will test the strength of your back. Just dig up a slice and put the green side down. Be sure to chop the slice. The better method calls for a rear-mounted rotary tiller. If your cover crop is too tall, again you may want to mow first. Mowing keeps the vegetation from getting tangled in the machine’s tines. Your garden soil should be ready for planting about two weeks after turning your cover crop under.
If your garden has been good to you all summer long by providing you and your loved ones with food or with beautiful flower bouquets, now is the time to repay your garden soil by planting a cover crop to use as green manure next spring.
Delaware State Extension