To grow healthy plants that produce bountiful harvests, we need fertile soil and a vibrant growing environment. One of the best ways we can create this environment is by using cover crops. Planted at strategic times throughout the year, cover crops are plants we grow to feed our soil rather than our bodies. For instance, planting a quick crop of buckwheat between summer and fall crops adds nutrients to the soil and provides protection from harsh summer sun. The many varieties of cover crops can suit the needs of nearly any garden. Knowing which crops serve which purposes can unlock benefits for any garden.
Why Plant Cover Crops?
• Leguminous cover crops “fix” nitrogen in the soil. An essential mineral necessary for vigorous plant growth, nitrogen is usually depleted over the course of a season. Legumes are able to absorb nitrogen from the atmosphere through a symbiotic relationship with a bacteria called Rhizobium. Once these plants are incorporated back into the soil at the end of their growing period, the nitrogen is converted into a form usable by subsequent plants.
• Cover crops add vital organic matter, increasing biological activity and humus in the soil. When cover crops are “turned into” the soil (cut down and incorporated into the soil) the residue breaks down, quickly or slowly depending on the structure of its fibers. Quick decomposers cause an increase in microbes that can lead to stronger plant growth and disease prevention, decreasing reliance on pesticides and fertilizers. Slow decomposers can add to the soil’s structure and water-holding capacity.
• Cover crops offer great weed control. Tall varieties such as sudangrass can be used to shade out weeds because of their height. Varieties such as clover and rye overtake and smother weeds.
• Cover crops aerate soil. If compaction is an issue in your garden, cover crops with deep root systems able to penetrate these soils create a looser environment for the harvest crops that grow afterward. If heavy clay is the issue, building up organic matter will increase air and water movement.
• Cover crops hold soil in place, beneficial where erosion is a problem. Through a strengthening network of roots and leaf and stalk growth, soil is protected from rain and runoff.
• Cover crops keep soil moist. Cover crop residue left on top of the soil increases water filtration and reduces evaporation; cover crops that get incorporated into the soil trap water and add organic matter.
Choose the Right Cover Crop
First, determine the specific needs of your garden. Is your garden space in need of nitrogen and microbial replenishing? Is it lacking organic matter? Are you losing topsoil to erosion from wind and water, or losing fruits and vegetables to weeds and pests? Once you’ve determined your need, consult a list of cover crops best suited for your area and narrow the list down based on your need. (See suggestions to follow or consult one of the resources listed in “Cover Crop Resources” later in this article.)
Next, determine the best time of year for planting. “Gardening with cover crops is a dance—timing is important. Ensure enough time to plant the cover crops and allow growth before they die or are killed for the next crop,” says Kirk Iversen, a certified professional soil scientist who works closely with Auburn University and the USDA National Soil Dynamics Laboratory. For example, some cover crops are planted in fall, die in winter and are followed by harvest crops in spring. Left on top of the soil, the dead residue provides a mulch that suppresses weeds until it’s time to plant spring crops.
Then, consider any additional traits that may affect the cover crop’s growth in your designated space. For instance, is the crop an annual or a perennial? Is it low-growing or tall and vigorous? How does it die and what does it take to turn it into the soil? From here, select the crop or crops that best fit your space and time available for growth.
To plant, prepare the soil by roughing up the top layer about an inch deep before broadcasting seed at the recommended spacing, usually found on the package. When broadcasting less than 1 pound of seed per 1,000 square feet, it may help to mix the seed with sand or screened soil before spreading. After sowing seeds, cover with a 1/2- to 1-inch-thick layer of compost or soil and use the back of a hoe or garden rake to tamp down the soil. Cover the area with a thin layer of straw or weed-free grass clippings and then water deeply. You may need to water the seeds for the first few days to get them growing.
A cover crop’s death is just as important to consider as its life. “Cover crops that don’t die in winter can quickly become weeds if left to set seed,” says Katherine Quinn, co-owner and operator of Full Circle Farm in Marion County, Arkansas. When the crop starts to flower, begin preparations for turning in the crop either by tiller or hand. Tilling is quick but can actually reduce the soil-building benefit of the crop by speeding up decomposition. Other options include chopping at the base and leaving cut material in place to decompose over time or gently turning in the material with a hoe or shovel. “After plants have been cut down or turned into the soil, allow two to three weeks for the material above the soil to dry out thoroughly and the turned-in matter below the soil to decompose, then plant new crops,” Iversen says.
Cover Crop Options
These crops are easy to grow, widely available and serve multiple purposes:
• Buckwheat and oats, strong growers during warm weather, and mustard, best grown during spring and fall, are fast-growing and easily fill the gap between harvest crop plantings. All offer a quick fix for soil in need of organic matter.
• If planted in early fall, vetch, an annual legume, will provide weed protection for fall crops, prevent soil erosion through winter, and continue to provide weed protection in early spring. Vetch fixes nitrogen in the soil. Cut it down at the base to plant new spring garden crops, and just let it lie to form a mulch that will keep soil moist.
• Clover, a perennial self-reseeding legume, can be used as a long-term living mulch that suppresses weeds when interplanted with other perennial harvest crops such as blueberries. As an added bonus, its flowers attract pollinators.
• If your garden is in need of large quantities of organic matter, Quinn recommends planting sudangrass, an annual cover crop, in early summer and then mowing it throughout the season to keep its hardy growth in check.
Cover Cropping Strategy
You can plant cover crops over an entire garden space for one season, and follow it with harvest crops next season. Or, if you don’t want to sacrifice garden space for an entire growing season, you can interplant cover crops as a living mulch between other harvest plants. You can also alternate specific garden beds over different seasons with cover crops and harvest crops.
Cover Crop Resources
You can order cover crop seed online, though shipping can get expensive. For less expensive alternatives, visit your local seed supplier or farm-supply cooperative. Seed may also be available at your local soil conservation office. Visit the Natural Resources Conservation Service.
“Managing Cover Crops Profitably,” available for purchase or free download from Sustainable Agriculture Research and Education (SARE).
Peaceful Valley Farm and Garden Supply Cover Crops Solution Chart
University of California, Davis SAREP Cover Crops Database
USDA National Soil Dynamics Laboratory publications
Local county extension