Cover crops, also known as green manures, are crops that are grown to improve and protect the soil. They’re generally not allowed to go to seed and before they get too big, the cover crops are mowed or tilled into the soil to enhance the organic matter and soil nutrients.  The cover crops also help to suppress weed development by providing competition against any weeds. A thick stand of clover or buckwheat leaves little room for any weeds to get established. Soil erosion and loss of nutrients thru leaching is also reduced because of the stabilizing effects of the cover crops root system. Cover crops can also provide a place for beneficial insects to reside, and their roots systems help to loosen and aerate the soil which improves rooting of future crops and promotes a healthy population of soil microbes. 

A wide variety of crops can be used as a cover crop, such as field peas, fava beans, crimson clover, buckwheat, fall rye, or hairy vetch to name a few. Good cover crops are generally annual crops that can be easily killed, chopped up and incorporated into the soil.  Most cover crops are also inexpensive to buy, making it economical to seed large areas.

Growing Cover Crops

A cover crop can be seeded any time there is a bare patch in the garden, but they are most commonly used in late summer, early fall, when the vegetable crop has been harvested and the soil is bare. Cover crops can also be seeded around existing vegetable crops, such as broccoli, that are close to maturity. After the vegetables are harvested, the cover crop is already established and growing.

To seed a cover crop simply broadcast the seed thickly over the soil and then rake or till the seed in to ensure good seed/soil contact. If the cover crop survives the winter, it’s important to kill them off in the spring before they get too big or else it is difficult to chop up all the plant material and get it incorporated into the soil. If the cover crop has gotten too big to till in, mow it and compost the excess plant material. Wait two to four weeks after tilling in a cover crop before seeding to allow for the decomposition of the dead plant material.

There are a wide variety of cover crops to choose from. Here are a few pointers to help you decide which cover crop is best for your situation.

Legumes

Legumes, such as crimson clover, fava beans, winter field peas and hairy vetch are excellent as cover crops because they are nitrogen fixers. Legumes symbiotic relationship with soil microbes allows them to capture nitrogen from the atmosphere and make it available to the plant, and thus build up the nitrogen reserves in the soil. Cover crops can add a significant amount of nutrients to the soil. An acre of fava beans tilled into the soil is equivalent to adding about 10 tons of manure. In order to ensure the best possible cover crop, coat the seed with the appropriate inoculant prior to planting. If hairy vetch is being used, remember that vetch seeds are toxic to chickens, and should be planted well away from any foraging flocks or mowed when flowering.  Hairy vetch is best used in the spring because it produces very little ground cover in the autumn, and puts on most of its above-ground growth in the spring. Consequently, it offers little ground cover during the erosion-prone fall and winter period. If fava beans are being used, buy the small seeded varieties that are much cheaper than the large culinary fava beans. Mow or till the fava beans into the soil before seeds start forming. 

Soil Builders

There are several cover crops that don’t fix nitrogen, but are excellent at growing rapidly, creating a living mulch that competitively crowds out weeds and produces a large amount of organic matter. Grasses such as fall rye or winter wheat can be planted in the fall and tilled in the following spring.  Oats can also be planted in the fall, but it often winter kills, and so is better used for a quick green manure crop in the spring. Other soil building crops include buckwheat, which produces broad leaves that shade out weeds. The flowers of buckwheat are also popular with honey bees. Buckwheat is not winter hardy and is ideal for quick green manure crops in the spring or summer. If you are going on a long summer holiday and your garden is going to be bare, a crop of buckwheat or oats will protect and enhance the garden while you are away, suppress weeds and make clean up easier.

Corn salad is another non-traditional cover crop. It’s winter hardiness and ease of tilling in the following spring make it a great candidate as a green manure, and you can snack on the leaves throughout the winter.
Sowing a mix of leguminous and grassy-type cover crops will increase the ground coverage, as well as provide some nitrogen to the following crop.

Pests Management and Cover Crops

Cover crops can enhance the garden thru more ways than simply enhancing the soil. Cover crops provide an environment for many beneficial insects. Some cover crops, such as oilseed radish or pacific gold mustard help to inhibit nematode pests.In a stable ecosystem there is typically a diverse variety of plants and animals, and it is this diversity that provides resilience and stability. In stable ecosystems, severe outbreaks of pests are rare because of the natural controls that exist to stabilize and bring a population of pests back into balance. Greater diversity often imparts greater stability. Cover crops are a great way to enhance your garden the natural way. They protect and build the soil and provide an environment for beneficial insects. They are an important and effective tool for a gardener to manage and enhance their garden soil organically. So, get out in the garden and start planting.