Do you leave your garden dormant in the winter until the following spring? Home gardens with bare soil and nothing growing are vulnerable to soil erosion, weed growth, and pest issues. Consider planting a cover crop this winter.
A cover crop typically consists of cold tolerant legumes, grains, or grasses that can help to prevent pest, disease and erosion issues and also improve the quality of your soil for the following spring. Growing cover crops in the winter makes your soil healthier and increases fertility. They are typically easy to grow, so there is little downside.
Cover crops are also considered a form of crop rotation, which is important for home gardeners. Planting the same vegetables over and over again in the same spot can quickly build up crop specific spore or fungal based diseases. The same plant type planted over and over in the same spot can draw up all the nutrients from the soil in that area of your garden, resulting in a poorer harvest or even a complete garden failure.
Cover crops, such as grains, grasses, and legumes, help prepare the soil for planting your garden in the spring or early summer. During the winter, the soil loses its nutrients and nitrogen can wash or drain away because there is no organic matter. Vegetable gardens in the spring and fall draw up soil nutrients during their growth period, so it is important to replenish the soil for the next year of gardening.
If you leave your soil bare over the winter, many beneficial organisms in the soil can be lost with no plants to keep them alive and active. Acting like “green manure,” cover crops help return many of those nutrients back to the earth and increase the tilth of your garden soil.
Before planting a cover crop, consider your soil’s needs. Do you want to increase carbon or nitrogen content, loosen compacted soil, prevent soil erosion, deter weeds, or improve overall soil quality? Some cover crops will improve biological and chemical properties of soil, while others may only serve to protect the soil’s physical properties.
Each cover crop comes with its own set of benefits and drawbacks, but one rule applies to them all; cover crops should not be grown in arid and semiarid regions. In these areas, the additional moisture cover crops use will further dry out soil, making their use counterproductive. If you are in an arid area, consider adding a heavy layer of compost each year, covered by mulch to keep it from washing away.
In general, winter cover crops should be planted no later than a month before the average date of first frost. If planted later, these crops will not be hardy enough to withstand winter temperatures.
When you decide cover crops are right for your garden and know what you’d like to accomplish by using them, you can begin to choose the crop best suited for your needs.
Rye as a cover crop
Rye improves overall soil quality by preventing erosion, adding organic matter, breaking up compacted soil, and improving soil aggregation. Rye develops a root system that is dense enough to retain saturated soil in the spring when the snow melts. Its root system can also trap and kill nematodes.
The ideal time to plant rye is in September to ensure the plants receive enough temperate weather to increase their chances of growth and survival. However, rye can be started later in the season than most other cover crops, and tolerates cold to temperatures below zero Fahrenheit. However, plants that are grown later in the fall are more likely to remain small and require a seeding rate three times that of those planted earlier in the season.
Planting seeds in drills, shallow holes beneath surface level, rather than on top of the soil provides them with space to establish deep roots. Roots that are too shallow risk frost heaving, according to Cornell University’s College of Agriculture and Life Sciences. [http://covercrops.cals.cornell.edu/fall.php]
In spring, pull rye from the ground, and allow it to dry. Once dry, use it for mulch. Rye is especially good mulch for plants set out as seedlings because it can reduce the germination of seeds by more than 90 percent.
The leaves are nitrogen-rich and can be cut several times throughout the season to return those nutrients to the soil. For best results, do not let the leaves go to seed.
Home gardeners often use annual rye grass as a cover crop.
Hairy vetch as a cover crop
Hairy vetch is a legume that increases soil’s nitrogen content. This makes it an ideal cover crop before planting nitrogen-hungry crops, such as tomatoes. Hairy vetch can be cold tolerant to temperatures as low as 20 degrees below zero Fahrenheit. Grow vetch with oats or rye for optimal benefits.
Hairy vetch can become a weed, so mow or till it before it produces seeds. Hairy Vetch may need the aid of Rhizobium bacteria to germinate, according to the Central Texas Gardener.
Rhizobium bacteria are beneficial to legumes, specifically, because they transform elements such as carbon, nitrogen, and sulfur from gaseous substances into a form plants can absorb. The Rhizobium bacterium enters through the hairs of a plant’s roots and infects the root system, forming nodules at the tips, where the nitrogen will fix. It is a symbiotic relationship that provides the Rhizobium bacteria with the carbon it needs to multiply and the legume with the nitrogen, or ammonia, it needs for protein synthesis. This method can be used for other legumes like hairy vetch as well.
Oats as a cover crop
Oats improve overall soil quality by preventing erosion, adding organic matter, and improving soil aggregation. For best results, sow oats six to 10 weeks before your local average date of first frost. Oats are less frost tolerant than most winter cover crops and are killed by temperatures below five degrees Fahrenheit.
However, oat’s low frost tolerance can be a benefit. Dead oats form their own mulch, which is typically well rotted by spring. If oats do not die during winter, mow and till them before seedheads appear in late spring. Oats should be incorporated early in spring to prevent nitrogen tie-up and moisture depletion. While oats are not effective at breaking up compacted soils, they incorporate into soil more easily than rye.
Winter wheat as a cover crop
Winter wheat improves overall soil quality by breaking up compacted soil, preventing erosion, adding organic matter, and improving soil aggregation. When it is well-established, winter wheat can tolerate cold to 25 degrees below zero Fahrenheit and prefers medium-rich loam soil.
Sow winter wheat at least six weeks before the average date of first frost. It is prone to frost heaving in the spring, which is when water beneath the soil freezes and gets pushed to the surface. Wheat is not a hardy winter crop, but it can serve as a nurse crop for crimson clover that is planted during the winter season.
Spelt as a cover crop
This grain can withstand colder and wetter soil conditions than winter wheat, which makes its chance of survival greater. According to Cornell University’s Department of Agriculture and Life Sciences, spelt heads earlier than wheat, which makes it ideal for maintenance and, later, harvest in the spring. Spelt heads should be removed before the plant flowers. Heads are the bulbs that come from the leaf shoots, nearest to the base of the leaf.
The Alternative Field Crops Manual (published by the extension programs of the University of Wisconsin and the University of Minnesota) states that spelt grows well in the Midwest because it thrives in the sandy soils native to the region. It can also withstand being grown in poorly-drained or nutrient-deficient soil.
Spelt seed, like most other low-growing grains, has to be seeded with a drill. A drill is a machine used to create small holes in the soil at a specific rate and spacing so that each hole is equidistant and identical in size. Then the seeds are released by the drill through tubes. Oats, wheat, and rye are seeded using the same method.
Crimson clover as a cover crop
Crimson clover is another legume that can be planted in the fall. While not particularly hardy, this plant has the best results if it is sown before mid-September. However, crimson clover can be planted as late as November. Legumes such as crimson clover add nitrogen to the soil and provide another source of organic matter when they are turned over in the spring for the cash crops to be planted. Crimson clover fixes approximately 100-150 lb N/ac/yr, which is more than most winter cover crops, with the exception of alfalfa.
Crimson clover is not drought tolerant. It needs well-drained, loamy soil and requires a soil pH of 5.8 or higher. If the soil pH is too low, minerals such as lime, phosphorus, or potassium may need to be tilled in. The soil always needs to be tested before seeding.
Some of the benefits of crimson clover include its herbal and medicinal properties. Its flowers attract bees, which increase crop pollination.
Other plants that are also recommended for use as cover crops are Austrian field peas, barley, black oats, garden peas, and ryegrass. These crops can be planted between Oct. 1 and Nov. 15 (depending on your gardening zone).
As a recap, test the soil pH before planting your cover crop. Legumes prefer a pH closer to neutral 7 and often need lime or other nutrients added in order to balance the pH for ideal growth. In “Cover Crops and Green Manures,” author Vern Grubiner suggests distributing about 100-200 lbs of lime per acre to balance the pH for ideal growth.
Till the soil before planting your crop, loosening the dirt about six inches deep; the best method for sowing grain is using a drill to get a consistent depth, distance and rate of seeding. Once the plant has reached maturity, after about four to six weeks of growth, be sure to prune—for the best results, they should not be allowed to flower or seed.
To prep the site for the summer crop, three weeks before you intend to sow the new set of seeds, turn the winter cover crop over, and allow it to decompose. Then till and follow the recommended instructions for your region when planting the next crop.
Megan Smith Mauk grew up in Texas, where she developed a reverence for all forms of life. In college, she became co-chair of the environmental coalition. She now lives with her husband, and their dog and cat, in Virginia.
Emily Nickles is a freelance writer and recent honors alumna of Texas Woman’s University. She was Editor-in-Chief of the student newspaper, The Lasso, for a year and was a page editor and reporter for three. Her senior year, Emily won the Sarah McIntire Award for Outstanding Capstone for her project titled The Lasso: A brief history 1914-2017.
Learn more about cover crops