What Are Cover Crops?

By Jordan Freytag

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Cover crops are seeds that are planted en masse for several reasons that benefit the soil and/or the local environment. Most often cover crops are grown by farmers in rotation with their cash crops to protect and rejuvenate the soil, a practice that goes back centuries.

Evidence of cover crop use can be found in different times and places throughout history: The Native Americans had a system of agriculture called “The Three Sisters” that utilized cover crop properties of beans, squash, and corn by planting them together, cycling nutrients through the soil, creating a synergy between the crops. Chinese Milk Vetch has been used for millennia as a cover crop in China, being planted just after a rice harvest in the same ground. And in Southeast Asia, soybeans have been grown as a cover crop in tea estates for generations. Even George Washington, a diligent farmer as well as statesman, was known for his “crops grown to replenish the soil.”

These examples throughout history and around the world, illustrate to us the various benefits and uses of cover crops. They attract pollinators, promote erosion control, preserve moisture, and suppress weeds when growing. When cover crops are mowed down to decay, nutrients are cycled back into the soil which subsequent vegetable crops profit from. Cover crops return nitrogen to the soil, but most notably through a process called “nitrogen-fixing” where the plants convert the nitrogen from the air into the soil.
In traditional agriculture, the practice of growing cover crops has changed little over the centuries. Today, fertilizers have overshadowed the use of cover crops, but they are making a comeback as large-scale growers are experiencing first-hand how growing cover crops not only keeps soils healthy and organic, but cuts down on the reliance of pesticides. Although the practice of growing cover crops can seem complicated, one just needs to become familiar with basic seed types and their role in soil health.
Legumes: Alfalfa, Clover, Chickpea (Garbanzo), Soybean, and Pea

Plants in the Fabaceae family, legumes are the primary nitrogen fixers of the cover crop world. While other seed types return nitrogen through decaying matter, legumes convert nitrogen from the air and return it to the soil with the aid of rhizobia bacteria. Legumes popularly require inoculation before planting, an easy process to ensure germination.
Grains and Grasses: Wheat, Rye, and Triticale

Grain cover crops are great protectors of soil while also scavenging for nitrogen and potassium. A terrific organic matter producer. The very same seed for making wheat flour, Hard Red Wheat, is a fantastic biomass producer.
Brassicas: Radish, Mustard

Not all brassicas work as cover crops, but mustards and radishes do. They help significantly control pests because they contain a higher amount of glucosinolate than other brassicas, a chemical compound that wards off harmful insects. When the plant cells are ruptured the plant releases the glucosinolate. Mustard and Radish are known for their rapid fall growth, which makes them an ideal weed suppressor.

Broadleaf Species
Includes both legumes and brassicas. Broadleaf crops are plants that produce wide protective leaves. Nearly all flowering cover crops are broadleaf species. If you are looking to attract pollinators with your cover crop, a broadleaf species is essential.
Cover Crop Mixes

Often, different varieties of seed are combined to create unique cover crop mixes. The idea is to harness several benefits to allow them to work in tandem, with each variety boasting their unique benefits, as found in the Garden Cover Crop Mix.
None of the varieties above are specific to spring or fall. The terms “spring” and “fall” cover crops are used to describe the time of year the cover crop seed is sown and grown rather than a classification of the seed itself. For example, mustard can be planted as a cover crop seed both in spring and fall.
Spring vs. Fall:

• Spring Cover Crops are often planted in the early spring and allowed to grow until a few weeks before planting when it is mowed down. Some varieties of cover crop seeds are sown in late fall after the frost and allowed to lie dormant until spring comes when they germinate in a process called “overwintering”.
• Fall Cover Crops are planted when summer temperatures are waning, giving the cooler season seeds time to germinate in the necessary autumn conditions. Once mature, usually around the first frost, these cover crop varieties are mowed down and allowed to decompose over winter.