Cover crops are green manures that create organic matter to feed the micro-organisms and earthworms in the soil. The microorganisms convert the organic matter into plant nutrients and increase tilth of the soil. They also enhance the soil’s water absorption ability, help create a soil network and develop biomass. They also guard against erosion.
Low-growing cover crops such as crimson clover or oats can be planted around existing plants to prevent weeds from germinating — that’s why they’re called “living mulch.” As the name implies, living mulch grows under edibles throughout the season, and can then be gently cut down and tilled into the garden soil in fall.
When the roots of the cover crops shed, they decline in the soil and develop deep underground organic matter without any tiller disturbance. Their flowers will attract beneficial insects and they can confuse or discourage predators at times.
Certain cover crops, such as hairy vetch or field peas, help in nitrogen fixation and others are classified as active accumulators of nutrients. Dynamic accumulators of nutrients obtain nutrients from deep within the soil. Their decay produces nutrients on the surface level of the soil as their leaves shed or their growth is chopped back. Cover crops are often broadcast in the fall over an empty field, and then in the early spring gently tilled under. Even they can be filled with fresh mulch or compost. The decaying crops are expected to release nutrients in time for a new season of seedlings, given a few weeks to decompose.
Other cover crops are best integrated in crop seasons as room holder in the greenhouse. Never leave a bed absolutely empty of plants I find it best practice. Even if I don’t get a chance to plant a new crop, I broadcast a few cover crop seeds over the soil easily. Before they can germinate, the cover crop can smother the weeds, avoid soil compaction and build up nutrients. Cover crops will serve as a buffer until winter when beds are cleared of debris and spent plants in the fall, and the root structure they produce will prevent nutrients from leaching out of the soil. Some cover crops, such as hairy vetch, during the cold season will go into dormancy, and then start growing again once the spring temperatures rise. Cover crops will raise the nutrient levels when new beds are added before the first edibles are sown.
Cover crops are simply the best way of improving soil, and at some point in the season they belong to any garden bed. You can’t really pick the “wrong” cover crop for your beds, but start with a couple of variety packs if this is your first season working with the cover crops. Each year add one or two choices to your list, and see what works best for your garden soil and environment. I have included a list below of some of my favorite cover crops.
Spread the seeds gently over the soil to plant a cover crop, and till them about an inch below the surface. Don’t grain down. In most cases, when the crop has just started to bloom, it is better to cut down the crop, just before the flowers have flowered or the crop has set seed. The crop will then produce both nitrogen and carbon, which will rapidly decompose when tilled back into the soil. The crop would require warm soil to decompose, so it is best to introduce the crop in early fall or mid-spring. When digged in, leave the crop to decompose for at least three weeks.