Cover crops are plants that are grown not for the food they produce, but for other beneficial work they do. Also know as “living mulches” or “green manure”, a cover crop is an essential part of sustainable agriculture. Cover crops help bridge the gap between removing matter from the field in the form of the harvest, and returning or conserving matter in the field by returning biomass, nutrients, and offering protection for existing topsoils.
Cover crops have been used for thousands of years to ensure the long term health and productivity of the land. Some 2,000 years ago, the ancient Roman poet Virgil writes in his book Georgics of sowing spelt following a cover crop of vetch and lupine. F. H. King documents, in Farmers of Forty Centuries, the ancient tradition of Chinese farmers who were “turning under Chinese clover to ferment as green manure, preparatory for the rice transplanting”. Use of cover crops is ancient agricultural wisdom that can still be applied today to the home garden.
The benefits of a cover crop to a home gardener are many. The questions isn’t why grow them, it is why would you not grow them. There are too many advantages a cover crop provides to pass up. A few examples include:
- Cover crops are used to enrich the soil. Green manures that fix nitrogen, such as fava beans and clover, work to take atmospheric nitrogen and fix it in the soil where the next crop can use it for food.
- A vigorous cover crop can be planted for weed control, smothering young weeds and starving them for sunlight before they can become established.
- Cover Crops create habitat for beneficial insects, who become allies in other areas in the garden by providing pollination and pest control.
- Living mulches protects topsoil from erosion. By breaking up and diffusing heavy rain, the cover crop prevents soil from washing away. A cover crop can also diffuse wind that can blow away precious topsoil. By breaking up air currents at the soil surface and keeping topsoil anchored with roots, a living mulch can protect a field or bed from ravaging winds.
- Cover Crops conserve soil moisture through reduced evaporation. By keeping the beating sun off naked soils when used as a mulch, cover crops form a protective layer that helps underlying soils retain moisture.
- Cover crops act as a buffer for soils, moderating swings in soil temperatures. Baking sun and exposed nights are moderated by the layer of living mulch.
- Cover crops can improve tilth and soil structure, in addition to breaking up compacted soils.
By planting cover crops, you can add a multitude of benefits to your growing system, all in a sustainable and environmentally friendly way.
Types of Cover Crops
There are many types of plants that can act as cover crops. To simplify, most can be sorted into three categories, legumes, grasses and grains, and other. Which you use and when will depend on your garden’s needs.
Legumes are plants belonging to the family Fabaceae. Vetch, fava beans, peas, and clover are examples of legumes. Legumes are prized for their ability to fix atmospheric nitrogen through a symbiotic partnership with bacteria. This process happens in nodules attached to their root system. When the plant dies, the nitrogen that was fixed in the nodules returns to the soil and becomes available to future crops. In addition to this wondrous ability, legumes can act as living mulches and as animal forage.
Grasses and Grains
Grasses and grains and grains such as sorghum-sudangrass, annual rye, and winter wheat are used to add biomass to the soil. These crops are killed before they go to seed, leaving roots and stubble to add organic material and improve soil tilth. Some grasses have extensive root systems that can penetrate deep into the soil, bringing nutrients to the surface that are left behind when the crop is killed. These roots also improve soil structure by aggregating soil particles and breaking up clumpy, compacted soils.
Grasses, with their tremendously extensive root systems, may relieve compacted surface soil layers. Sorghum-sudangrass can be managed to powerfully fracture subsoil. - Marianne Sarrantonio
Buckwheat, mustard, turnips, and oilseed radish are examples of cover crops that aren’t legumes or grains and grasses. They can be planted to attract beneficial insects, deter pests, or shade out competing weeds. However, some have challenges all their own. According to Charlie Nardozzi with Edible Landscaping, oilseed radish “kills nematodes when tilled into soil, but may harbor brassica-family diseases”. Choose your cover crops wisely according to your garden’s needs, and you can make this group of crops work hard for you.
Cover Crop Strategies
There are several strategies to using cover crops. The Minnesota Department of Agriculture shares:
- A winter cover crop is planted in late summer or fall to provide soil cover over winter.
- A catch crop is a cover crop planted after harvesting the main crop, primarily to reduce nutrient leaching.
- A smother crop is a cover crop planted primarily to out compete weeds.
- A green manure is a cover crop incorporated into the soil while still green, to improve soil fertility.
- Cover crops can serve as short-rotation forage crops when used for grazing or harvested as immature forage (green chop).
Timing is Everything
Cover crops can be planted from spring through late fall. The type of cover crop and it’s purpose will determine the best times to plant. For example, fava beans – grown for their nitrogen fixing abilities – can be planted in the fall. They take a long time to mature and can handle the cooler temperatures in a mild winter climate. By spring, as they begin to flower, fava beans can be turned under and the soil conditioned for the spring crop.
Rye, however, can be planted at different times of the year. According to the University of Connecticut, “Rye is superior at capturing nutrients in fall and winter and provides a more persistent weed suppressive mulch in summer.” Planting rye at different times will encourage different results, enabling you to fine tune your home garden and soil management strategy.
By getting to know what types of cover crops serve what purposes, you will be able to insert them into your crop rotation for maximum efficiency. Click on the image below for a handy fact sheet on when to plant cover crops.
Table By: R.L. Rackham and R. McNeilan
Born To Die
Part of the job of many green manures is being returned to the soil, adding nutrients and biomass and building fertility. This is all accomplished by killing the crop before it reaches maturity. In other words, cover crops are born to die.
When the time comes to recycle a cover crop, some can be cut and mulched in place, such as buckwheat or hairy vetch. This involves cutting down the crowns of the crop as it begins to flower, and leaving the tops in place as a mulch. The roots die, adding organic material to the soil and making passage through the soil easier for future crop roots and beneficial soil organisms. Other crops, such as rye, can be mowed and then tilled into the soil. For cover crops of this type, it is best to give the soil about four weeks to condition before planting the next crop.
Each crop requires a different strategy, know your crop and what work it will take to re-incorporate it for the maximum benefits.
The seeds of many cover crops are easy to find. A local garden sector should carry common seeds, such as clovers. Amazon.com has a wide selection of seeds as well. You can also try a local seed and feed store that carries agricultural supplies – they may be able to get seeds in bulk quantities and competitive prices.
Give Cover Crops A Try in Your Home Garden!
Don’t let a season go by without leveraging the advantages of a cover crop. Now is the perfect time to start planting to enrich your home garden’s health. Make cover crops an important part of your home gardening plans.
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