Cover Crops: Add Some Oomph to Your Soil

Add Organic Matter

Adding organic matter to the soil prevents it from crusting over, keeping it loose and receptive to water infiltration and aeration. The addition of organic matter can also attracts soil microbes and earthworms that contribute to soil nutrition and improve the soil structure.

Reduce Erosion

During periods of heavy rainfall or moderate drought, cover crops help prevent erosion by anchoring the topsoil with their roots.

Add Nitrogen

Cover crops are an excellent solution to managing nitrogen in the soil. Nitrogen is a major component of chlorophyll, which plants need to perform photosynthesis in order to grow. Nitrogen is a difficult nutrient to manage in agricultural systems because plants can only use it when it is available in a specific chemical form (NOT the form prevalent in the atmosphere) and it easily leaches out of the soil during heavy rainfalls if it isn’t fixed inside the tissue of a plant.

Legumes (a family of plants that often have pods—beans, peas, etc.) can trap significant amounts of nitrogen that can later be used by other crops. A type of bacteria that lives in the plants’ roots converts atmospheric nitrogen into a form that the legume can use for its own growth. When leguminous cover crops begin to decompose, soil microorganisms convert the nitrogen in their tissue is into a form (nitrate) that subsequent plants can use.

Non-leguminous cover crops (typically grasses), can also help to keep nitrogen available by taking in nitrogen already present in the soil that would otherwise be lost to leaching. The nitrogen is assimilated into the plant tissue and when the cover crop begins to decompose, it is released back into the soil for subsequent crops to use.

Reduce Weeds

While cover crops are growing, they suppress the growth of weeds through competition and shading. If the cover crop is killed and left on the soil as mulch, it can continue to fend off weeds by blocking sunlight. Some cover crops also release weed-suppressing chemicals (crimson clover and hairy vetch have been found to do so).

Attract Beneficial Insects

Cover crops can attract insects that will benefit subsequently planted crops when the cover crop dies. The insect population has time to expand during the cover crop’s lifetime in order to reach a number capable of managing the pests that plague subsequently planted crops. Unfortunately, cover crops also have the potential to attract pests that can harm subsequent crops.

Jay Reimer, “nitrogencycle” November 30, 2010 via Flickr, Creative Commons License.

The first step to reaping the benefits of a cover crop in your garden is to pick which plant best fits your needs. Once you’ve figured out the time of year that’s most convenient for you to try a cover crop, check out these great options that are beneficial in a wide range of gardens, from the folks at Mother Earth News:

Summer

During the summer, buckwheat is in a class by itself as a cover crop. Seeds sown in moist soil turn into a weed-choking sea of green within a week, with many plants growing 2 feet high or more and blooming in less than 30 days. Should you need to reclaim space that has been overtaken by invasives, buckwheat can be your best friend. Fortunately, even mature buckwheat plants are as easy to take down as impatiens — simply pull the succulent plants with a twist of the wrist, or use a hoe or scythe to slice them off at the soil line. You can let the dead plants die into a surface mulch and plant through them, gather them up and compost them, or chop them into the soil.

In late summer, while the soil is still warm, you have a fine opportunity to try barley, a fast-growing grain that’s great for capturing excess nitrogen left over from summer crops, which might otherwise leach away during the winter. Barley often suffers or is killed altogether colder areas, but this can be good! The dead barley residue shelters the soil through winter, and dries into a plant-through mulch in spring in cold zones.

Fall

Early fall is the best time to grow the dynamic duo of soil-building cover crops — oats mixed with cold-hardy winter peas. When taken down just before the peas start blooming in spring, an oat/pea combination cover crop is the best way to boost your soil’s organic matter and nutrient content using only plants. On the down side, one or both crops can be winter-killed before they have a chance to do much good in colder areas, and in more hospitable climates it will take some work to get the plants out of the way in spring. Do it by mid-April, because the job gets tougher as the plants get older. Cut or mow them down first, and then pull and dig your way through the planting. A heavy-duty chopping hoe works well for this

Hairy vetch needs a good head start on winter, too, but it’s fairly hardy and gives a huge payback in terms of soil improvement, and saved time and labor. Unlike many other cover crop plants, you can quickly kill hairy vetch by slicing just below the crown with a sharp hoe. When hairy vetch is beheaded about a month before it’s time to plant tomatoes and peppers, you can open up planting holes and plant through the dried mulch — no digging required.

Late fall is not a lost season for cover crops, but in most climates you’re limited to cereal rye, the cold-hardiest of them all. Rye will sprout after the soil has turned chilly, but be sure to take it out early in spring, before the plants develop tough seed stalks. Or let your chickens keep it trimmed; leave the birds on the patch longer in spring and they will kill the rye for you. If you’re looking for a cover crop you can plant in October for cold-season poultry greens, cereal rye is probably the best choice.

Mike_tn, “Hairy Vetch flowers” May 5, 2006 via Flickr, Creative Commons License.

Once you’ve chosen a cover crop, the rest of the process is fairly easy:

1. Planting

In many cases, cover crops germinate very easily and will grow even if they’re just strewn onto the ground. Make sure, however, that they are somewhat incorporated into the soil to discourage birds from snacking.

2. Care

Cover crops are typically low-maintenance, but some grasses need to be mowed to remain manageable. It is important to water cover crops, even during times of drought. Failing to do so might cause the crop to die, leaving the dry soil vulnerable to erosion.

3. Killing

You must kill your cover crops before they set seed and, in some cases, become invasive. The best time to do so is when the plant is flowering or when the seed heads emerge on grains. Annuals can be killed by cutting at the base of the plant.

Some cover crops can be mowed with a lawn mower or a weed trimmer, depending on their height. After mowing, wait a day or two until the leaves and stems dry down, and then incorporate them into the soil. After turning under a cover crop of grasses, wait two to three weeks before planting vegetables or flowers, in order to allow the plant to decompose and release its nitrogen. Certain cover crops release chemicals that inhibit seed germination—a plus for preventing weeds, but a problem for planting crops!

Photo courtesy of HOMEGROWNer Brian Gandy.

Read more:

• HOMEGROWNer Megen Hall on how to integrate a cover crop into your planting schedule without taking valuable garden space out of production.
• A guide to cover crops from Cornell University’s College of Agriculture and Life Sciences.
• A listing of cover crop varieties and their requirements for growth from the University of California Sustainable Agriculture Research and Education Program.
• Great tips and trick for cover cropping from Ontario’s Ministry of Agriculture, Food and Rural Affairs.
• A video of Don Forgey’s success in adding a cover crop at Cronin Farms in South Dakota to enhance his no-till crop system.