10 Winter Cover Crops to Recharge Your Soil This Winter

Fall is one of the busiest times of the year for gardeners. It’s time to finish the harvest, store your garden supplies and put your garden to bed for the winter. This fall, consider planting a cover crop — sometimes called green manure — to the list as well.

Winter cover crops have been used mainly by farmers to protect and nourish their fields.  However, in recent years, backyard gardeners are realizing the value of cover crops and the  benefit of them for their gardens. While the gardener is taking a much-deserved break while planning for the next year’s garden, the cover crop can be hard at work improving the soil, adding nutrients and getting the ground ready for the spring.

What Are the Benefits of a Cover Crop?

Cover crops can be used in any garden, including raised bed gardens. The cover crop seeds are usually fast germinating and fast growing. The purpose of a cover crop is to literally cover the garden with a living blanket of plant matter to sustain soil life. Here are some of the benefits of a cover crop: 

• Preventing Soil Erosion — When you remove the plants that grew through the summer, you expose the soil to the elements. Without a cover crop, you risk losing precious soil from your garden due to wind, rain or snow.
• Preparing Soil for Spring — When the cover crop is incorporated into the soil, there will be an increase of organic matter and nutrients in the spring. This is especially beneficial to gardens with sandy soil. Sandy soil allows water and nutrients to be flushed away when there is a heavy rain. By adding organic matter, the absorption of water and nutrients is much more stable.
• Decreasing Compaction — Cover crops help to avoid compaction in your soil, especially clay soils, by improving root, air and water penetration.
• Fostering a Healthy Habitat — Cover crops have the benefit of increasing the activity of earthworms and beneficial microorganisms and providing a habitat for beneficial insects.
• Avoiding Weeds — By nature, weeds grow where they find space. A cover crop will help to reduce weeds by simply crowding them out.
• Feeding Pollinators — Some cover crops can provide nectar or pollen for the pollinators in late fall, or early spring when most other flowers are not blooming when you allow the ground cover to grow and flower.

There are many different cover crops to choose from and each will offer different benefits. Some will grow better in your grow zone than others. You may have to experiment a little to decide which ground cover is best for your situation. There is no reason that you can’t divide the garden up or plant each raised bed with a different cover crop so you can experiment which will work best for your garden.

For the home gardener, an annual cover crop is preferred over a perennial. The annual will either complete its growth cycle by spring or it will die in the cold temperatures of winter. Perennial cover crops are more difficult to dig under in the spring and can be a problem to eradicate from the garden. 

Cover plants should be planted in late summer or early fall in the north. In the south, you can plant as soon as you finish harvesting. Cover crops need at least four weeks to get established before the first frost. If you live in the north where the first frost can come early in the fall, consider planting the cover crop immediately after harvesting a section of the garden or you could seed the cover crop between the remaining crops.

How to Decide What Type of Cover Crop to Use

The four most common cover crops are Red Clover, Hairy Vetch, Winter Rye and Oats. The choice should be determined by the grow zone you live in and the primary reason you are planting the cover crop, including:

• Addressing Nitrogen Levels — If you need to replenish the nitrogen in your soil, legumes are your best choice. Legumes such as clover and soybeans have the ability to fix nitrogen in the soil. Legumes carry a bacteria on their roots that can take nitrogen from the air and store it in nodules on the roots of the plant. Think about the farmers who alternate corn and soybeans in their fields each year.
  • Corn is a heavy nitrogen feeder when it grows the large cornstalk with lots of leaves. Soybeans are nitrogen fixers and will replenish the nitrogen for the following year. A recent study determined that by using a cover crop, you can reduce the loss of nitrogen from the soil by up to 97 percent.
• Breaking Up Compact Soil — If you need to improve a heavy or clay soil, oats and barley will break up the soil and improve its permeability; however, you will have to add nitrogen in the spring. Another option is to plant a mix of cover crops like ryegrass and clover at the same time. The ryegrass will improve the soil while the clover is adding needed nitrogen.
  These mixes are readily available for purchase, or you can mix your own. Another good choice for clay soil is daikon radishes. These grow an extra-large root that helps to break up the soil much deeper and adds significant organic matter.
• Firming Up Sandy Soil — If you need to improve a sandy soil, using a cover crop will add large amounts of organic matter to your soil which will help hold moisture as well as nutrients.

How Do You Sow a Cover Crop?

Till or loosen the top few inches of the soil and then lightly rake to give a good planting surface. Simply hand scatter the seeds over the area and rake in if the seeds are small. If the seeds are large, plant in rows that are close together. Cover with soil equal in depth as the size of the seeds and then tamp down gently with the back of the rake. Lightly water and cover with a thin layer of straw to protect the bed from heavy rain and wind while the seeds germinate. 

If you are planting legumes, you will want to use inoculant to guarantee the nitrogen fixing process. The inoculant is a bacteria called Rhizobium leguminosarum that causes the beans or peas to form the nodules and store the nitrogen. Without these bacteria, the plants may not have the nitrogen they need to grow as well as replenish the nitrogen in the soil. 

There are two ways to apply the inoculant. It can be added right to the soil as you plant the seeds, or you can apply it to the seeds directly. Simply pour the seeds into a water-filled dish to wet them and then roll them in the inoculant. Some gardeners add one part corn syrup to 10 parts hot water to the inoculant. Let it cool before using and then add the seeds, as this helps the inoculant to stick to the seeds.

Besides the rake and seeds, the inoculant is one of the only indoor garden supplies you will need to grow a cover crop. 

What Happens with Cover Crops in the Spring?

When early spring arrives and your perennial cover crops resume growing, many will want to flower and then set seed. The danger is that your cover crop could become a weed-like plant. The annuals will be dead from the cold, with some lying on top of the ground and others still standing. You now have three options: use the plant matter as a mulch, add the plant matter to the compost bin or dig the plant matter into the soil. 

Regardless of which you choose, it is best to cut the organic matter into smaller pieces so it can be utilized in the soil sooner. Depending on what type of cover crop you planted, you can chop it up with garden shears, a string trimmer or you can even use a mulching mower. If your cover crop is a nitrogen fixer, don’t pull the roots out of the ground. Once you have chopped the plant material, remove it to the compost bin. You can also leave it on the surface of the soil and simply move it over when the time comes to allow planting. 

If you want to improve the soil with the organic matter, either work it into the soil with a garden fork or use a rototiller. You should wait two to three weeks before you plant so the breakdown of the material can proceed and the benefits of the organic matter you added — as well as the nitrogen fixing — can set in.

Which Type of Cover Crop Should I Choose for My Garden?

These are some cover crops you may want to consider trying in your garden:

Hardy Legumes

These cover crops will add organic matter to your soil, and they will increase the nitrogen. You should be sure to mow these down before they flower in the spring.  Some hardy legume options for you to consider include:

1. Crimson Clover—Grows 18 inches high and is hardy to 10 degrees. Crimson Clover will fix nitrogen and attract bees. Be sure to mow before it goes to seed or it can become weedy.
2. Berseem Clover — Will grow one to two feet tall and will regrow after cutting. This type of clover is hardy to 20 degrees and produces large amounts of nitrogen.
3. Hairy Vetch — Hardy to -15 degrees, this is the hardiest annual legume that grows to two feet tall and is proficient at fixing nitrogen in the soil. This plant can have so much top growth that it is hard to turn over by hand. You will need a good mulching mower and probably need to be prepared to till the soil after it is chopped.

Tropical Legumes

These legumes need warm weather to grow. They can be planted as a cover crop in the southeast and southwest parts of the country. They will produce a large amount of organic matter and increase the level of nitrogen in the soil. Northern gardeners will need to plant this as a summer annual.

• Some tropical legume options for you to consider include:
  1. Cowpea — This legume prefers humid warm temperatures and is hardy to 32 degrees. Cowpeas will grow one to two feet high and can be used to stop erosion and block out weeds.
  2. Sunn Hemp — Grows five to six feet tall and needs the same growing conditions as corn. Hardy to 28 degrees, this cover crop needs to be cut up before the stem becomes woody.

Grasses

Grasses don’t add nitrogen to the soil, but they do help if you have compacted soil and they tolerate cold temperatures. Grasses are great for controlling erosion, but these are annuals so cut them down before they set seed and/or till them under. Some grass options for you to consider include:

1. Winter Rye — Grows four to five feet tall, this is the best grass if you live in the north as it will tolerate temperatures as low as -20 degrees. It is a great choice for preventing erosion from wind and water. This grass has very fibrous deep roots and can be difficult to turn over in the spring. Use a mulching mower and till the organic matter into the soil.
2. Oats — Grows two to three feet tall, this grass is tolerant of wet soil and temperature as low as 10-20 degrees. This cover crop is great at preventing soil erosion and it loosens heavy soils.
3. Barley — Grows two to three feet tall, this grass is tolerant of dry soil and temperatures as low as 0-10 degrees.

Other Annual Cover Crops

These cover crops will produce a lot of organic matter, but they will not increase the nitrogen levels. Some other cover crop options for you to consider include:

1. Buckwheat — Grows one to three feet tall and is tolerant of temperatures down to 32 degrees.
2. Brown or Black Mustard — This plant has a strong taproot but can become a problem weed in the garden. Tolerant of temperatures as low as 0 degrees, this plant will grow to one to three feet tall. Mustard plants are attractive to the bees. 

Let this be the year that you use a cover crop to protect your garden soil and improve its condition. Decide which one will meet your priorities or even try a mix of different cover crops in the same area. The benefits could be a game changer in your garden.