Cover Crops For the Garden

Unlike garden crops planted for their delicious edible outcomes, cover crops planted between growing seasons boost soil health and ensuing vegetable production—a sort of crop’s crop. Planted in rotation with edibles, cover crops improve soil by adding and retaining minerals and organic matter. They also reduce soil erosion, and keep soil loosened and aerated, while increasing water infiltration and helping suppress weed growth. Some even attract beneficial insects.

Non-Legumes and Legumes

Cover crops divide roughly into two categories: non-legumes and legumes.

The best non-legume cover crops have fibrous root systems that reduce soil loss and take up nutrients that might otherwise leach out of the soil over the winter. Plus, their energetic growth suppresses weeds. Popular non-legumes for gardens are buckwheat; grasses such as oats, winter rye, barley and Sudangrass; and several plants in the brassica family.

The main advantage of legume cover crops is their ability to fix nitrogen gas in the atmosphere into nitrogen that can be used by plants. Most-used legume cover crops for the garden include crimson clover, hairy vetch and cowpeas.

While both types of cover crops contribute organic matter to the soil, non-legumes produce more of this biomass. Chopping or cutting back cover crops before they go to seed is the best practice to avoid unwanted reseeding. The cut organic matter is left on top of the soil as mulch or tilled under.

As mulch, cover crops continue to suppress weeds and add nutrients to the soil as they decompose. If you till non-legume biomass into the soil, do it several weeks before planting garden crops, because the actively decomposing materials “tie up” nutrients the newly planted crops need.

When and What to Plant

Summer cover crops are planted following harvest of short-season crops and cut prior to planting. Buckwheat provides excellent weed suppression, but it must be cut soon after it begins flowering to avoid unwanted reseeding. The legumes cowpeas and crimson clover are good for summer, and can be planted together with non-legumes for weed suppression and added nitrogen.

Winter-kill cover crops are planted after garden crops are harvested, then killed by freezing temperatures. The following spring, you can plant early-season greens and veggies right into the resulting mulch. Winter-kill cover crops include oats, brassicas and field peas for USDA Zone 7 and colder. Crimson clover will winter-kill in Zone 6 and colder.

Overwintered cover crops are planted late in the season. They are seeded even as late fall crops are being harvested and then live through the winter, providing weed suppression and ample biomass when chopped down before flowering the following spring. In temperate climates, good overwintering crops are winter rye, hairy vetch and crimson clover. In far northern regions, winter cereals such as rye, wheat and triticale are good choices.