Cover Crop Gardening
Green manuring – the growing and turning under of crops to fertilize and improve the soil – is an age-old practice that is gaining popularity again. Why raise green manures? Why plant cover crops? The answer is simple. All these crops will improve the soil. They add something valuable to it.
Cover cropping and crop rotations are two gardening practices that can protect and rejuvenate the soil. Mixed plantings of two or more species can enhance biological diversity. Growing in the same place year after year exhausts soil nutrients and exacerbates pest problems through eliminating habitat for natural enemies and by making it easy for insects and disease to spread from plant to plant.
Cover crops such as buckwheat, oats, and winter rye work to protect the soil from erosion, control weeds, and builds organic matter. Legume cover crops, such as peas, clovers, cowpeas, fava beans and vetch, have the additional benefit of storing nitrogen for future use by other plants.
Cover crop plants are often used in combination, such as sowing a legume such as peas or vetch with a grass such as winter rye or oats. The legumes build nitrogen while the grass provides a natural trellis for the legume. A diverse habitat is created for beneficial insects and soil organisms. Te enhance the attraction of beneficials, you can interplant wildflowers and other insectary plants with the cover crops.
Planting and Harvesting a Cover Crop
To sow a cover crop it is necessary to prepare the soil by tilling or raking up the surface to be able to cover the seed. After the soil is prepared, broadcast the cover crop as evenly as possible. The seed can be covered by raking lightly into the soil, do not bury too deep. Keep the bed moist until the crop is established.
Before planting your summer crops, mow and chop the cover crop material into the soil. Turn the soil about 4 to 6 inches. It is best to wait at least two weeks for the “green manure” to break down before planting. A layer of compost maybe added into the cover crop before it is turned to help the decomposition process. If the soil is heavy, incorporating earthworms helps speed up the process of decomposition.
Legumes and Nitrogen Fixation
Nitrogen is stored in legume nodules on the roots. Once the legumes are turned under, the nodules provide an essential plant nutrient for subsequent crops.
“Which cover crop should I grow?”
No singer cover crop will work in all situations, first identify the objective. A cover crop that fixes a great deal of nitrogen may fail to prevent leaching of nutrients already present in the soil. If a lot of composted manure is used there may already be plenty of nitrogen available in the soil. If this is the case, you may choose a grass like winter rye that can take up the nitrogen and turn it into increased biomass. Choose a cover crop that grows well in your locale. Cover cropping is still better than leaving the soil exposed to the elements.
Vetch
Cold-tolerant, adaptable and vigorous winter annual legume. Plant in late summer or early fall. Vetch is slow to establish, but very prolific spring growth. Dense, viny growth, 2-3 feet high. Plant 30 lbs/acre or 12 oz/1000 sq. ft.
Red Clover
This winter annual legume is an excellent choice for controlling weeds and protecting soil during the winter. It produces stunning red flowers from mid to late spring. Plant 20-30 lbs/acre or .5 to .75 lbs/1000 sq. ft.
White Clover
The white clover plant is a low, creeping perennial often found on lawns. However, it is increasingly being used as a cover crop. It is a good green manure, tolerating excessive moisture, and producing rich organic matter.
Crimson Clover
This clover is popular where winters are relatively mild, and where it is planted in the fall. It makes rapid growth in the spring, and decomposes rapidly when it is turned under, so it contributes much organic material to land that is quickly ready for such warm season crops as corn, beans, melons and squash.
Fava Beans
This medium-sized fava bean survives winter temperatures down to 10 degrees. Fall plantings grow up to 6 feet tall. Can also be planted in early spring and does best where cool, moist weather persists for 2-3 months. Legume. Plant 150 lb/acre or 2.5-3.5 lb/1000 sq. ft.
Non-Legumes
Buckwheat
This broadleaf summer annual grows extremely rapidly, producing flowers in 5-6 weeks and growing 3-6 feet. Grows in acidic and low fertility soils. An ideal smother crop resulting in a nearly weed-free, loose seedbed. Attracts numerous beneficial insects and can make soil phosphorus, calcium and potassium readily available. Plant 50-100 lbs/acre or 1.2-2.5 lbs/1000 sq. ft.
Winter Rye
This is the most cold-hardy and productive annual grass and it tolerates a wide range of soil conditions. Plant any time for early to late fall. Germinates and grows quickly to a height of 4-5 feet. Its fibrous roots markedly improve soil structure. Commonly grown with peas or vetch to provide structural support. Plant 80-1500 lbs/acre or 2-3/5 lbs/1000 sq. ft.
Prepared by Kim Schleis, WSU Master Gardener and Kim’s Garden’s & Nursery
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