Cover Crops in a Garden

Cover crops can have a wonderful fit in gardens. We have been using cover crops in our garden in Pierre for a number of years now.

Cover crops consist of a broad range of plant species. The range of species falls into four categories; cool season grasses, cool season broadleaves, warm season grasses and warm season broadleaves. Cover crops can be grown on their own or they can be grown in a mix that includes species from one, two, three or all four of these categories.

Photosynthesis is a process that takes sunshine, water and CO2 and produces food. The carbon from the CO2 is used as a building block for the plants and the oxygen is released back into the air. The carbon used to build the plant is eventually released back into the soil and contributes to soil organic matter. This happens in a couple of different ways. One way is through plant degradation. But plants can also exude a sweet, high carbon exudate through their roots. Some soil microorganisms feed on this exudate and in return provide the plants with needed nutrients.

Cover crops can provide other benefits in addition to feeding soil microorganisms and building soil organic matter. Their roots also create channels in the soil that facilitate air and water exchange. Soils should have 50% pore space. They can act as a mulch, reduce surface crusting and surface soil temperatures. They compete with weeds and create habitat for beneficial insects and pollinators. Careful species selection can also break disease cycles.

You might wonder how a cover crop can fit in your garden? Cover crops can be planted in areas where early crops have been harvested. Lettuce, radish, spinach and peas all mature relatively early. These are areas where adding a cover crop, after those crops are finished, can be a good fit. Even later in the summer as beans, and other mid-summer crops mature, it is not too late to seed a cover crop. We plant almost half of our garden to a cover crop each year, while the other half grows our vegetables.

Cover crops usually consist of a mix of plant species but not always. Because most of our vegetable species are broadleaf plants (tomatoes, peas, lettuce, pepper, squash etc.) we choose to include a high percentage of cool season grasses such as oats, barley, and spring or winter wheat, in our cover crop. These are crops that grow well in the late summer and fall. Also, they are grasses, and therefore will not host the same disease and insects that can be problems in vegetable plants. The grass species will not bridge pests to our next vegetable garden. This is important in our garden because we grow a lot of tomatoes and we do not use tillage to break down last year’s garden residue.

Adding a few legume seeds, such as peas and lentils can provide some free nitrogen since these crops are able to take atmospheric nitrogen and convert it to a plant useable form. These also grow well into the fall. Another species that you may want to include in small amounts would be flax. The flax will help attract pollinators to your garden.

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