This fact sheet instructs home gardeners on how to select, plant, and control cover crops. It reviews the benefits and challenges of introducing cover crops into the garden. Beginners and advanced gardeners alike will find information on how to introduce cover crops into their garden depending on their skill level and desired management level. This fact sheet provides basic, fact-based information that is not readily available to home gardeners on how to utilize cover crops despite there being much interest in the topic.
Cover Crops in the Garden
Cover crops can be an excellent way to build soil organic matter, recycle nutrients, and control weeds. However, careful consideration of all the factors associated with cover crops is necessary before planting to ensure they help, rather than hinder, the main garden crops.
While cover crops offer many benefits, results will vary depending on soil type and condition. Starting organic matter levels, tillage practices, fertilizer and compost additions, and crops grown will all impact the introduction and management of cover crops. Further reading into these impacts is available under the resources section of this fact sheet.
Types of Cover Crops
When deciding which cover crop to plant, gardeners should consider:
- goals for the cover
- cost
- control strategies
Using leftover brassica seeds, such as kale and radish, is a good way to start. They will winter-kill or can be controlled through tillage or by pulling the cover crop plants in the spring. Table 1 has a list of cover crops by species and a description of their main benefits.
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Grass-like cover crops are best for building organic matter and soil tilth because they have such abundant root systems. Oats are inexpensive and will winter kill during most Ohio winters. Brassicas—especially the larger radish varieties—fight soil compaction. Legumes can add nitrogen to the soil for next year’s crop. The amount added depends on the species and amount of biomass accumulated. Research conducted in field crop scenarios showed a range of 29 to 160 lb. of nitrogen produced (Ozorio & Basche, 2022). Most cover crops take up excess nutrients not used by the garden crops. Cover crops also release nutrients over time as they breakdown the following season. As Figure 1 shows, a mixture of cover crops can be used to achieve multiple benefits.
Weed Control
Cover crops offer weed control through competition and shading of weeds. Common practice is to plant cover crops after vegetable crops to control winter annual weeds. Cover crops that grow into spring provide continuous weed suppression.
Although it requires a higher level of management, cereal rye is a great option because it can be seeded late into the fall. It also continues to grow in the spring, providing additional benefit. This continual growth, however, must be controlled. See the Control Methods section for options.
The earlier the crop is killed, the less weed control it offers. Despite how abundant the foliage looks, if the stem has not elongated, the foliage breaks down rapidly once killed. Note that cereal rye does inhibit the germination of small seeds. Research has shown that lettuce emergence drops to 50% when planted in cereal rye that is 50 days old at the time of termination (Barnes & Putnam, 1983). This adds to the weed-control benefit of cereal rye but can prevent small-seeded vegetables, such as lettuces and carrots, from germinating. This effect lasts a few weeks after termination.
Planting
After vegetables are harvested, most cover crops can be planted until the end of September. These cover crops can be planted through mid to late October:
- winter wheat
- cereal rye (see Figure 3)
- rapeseed
- kale
When planting is done later in October there is a greater risk for frost damage. Two cover crops gardeners should avoid are annual ryegrass and vetch. These can be difficult to control in Ohio.
Cover crop establishment can easily be accomplished by planting into rows with a hoe or broadcast application by hand or spreader. If the soil is hard, tillage and/or raking to create better seed-to-soil contact results in greater germination.
Control Methods
Starting with a cover crop that is likely to winter-kill may be the least intimidating way to introduce cover crops into the garden. Note that even some cover crops that typically winter-kill may survive if planted in mid-summer and/or during a mild winter.
Remember that the longer cover crops can grow, the more benefit they provide. Also, allowing the residue of dead plants to break down in the garden builds organic matter. The caveat is that plant breakdown can use nitrogen in the soil, so additional nitrogen may be needed at the beginning of the season. One to 2 pounds of a 10% nitrogen product per 100 square feet should mitigate any negative effects.
Glyphosate application: This allows cover crops to remain on the surface as a weed and moisture barrier and controls many existing weeds. It is also the least labor intensive. Always follow pesticide label directions. Figures 4 and 5 show a glyphosate application to cereal rye over a four-week period.
Pulling: For small areas, or as a last resort, pulling can be used to control cover crops. If plant material is completely removed from the garden, the organic matter benefit will be reduced. This is also the most labor-intensive and time-consuming method.
Smothering: Cover crops can be killed by covering them with a barrier such as cardboard. This offers an herbicide-free option for no-till gardens.
Tilling: This is an herbicide-free way to control cover crops. Ensure the tiller can process the density of the cover crops it encounters. Tilling removes existing weeds but does not help with weed control and moisture retention later in the season.
Crimping Cereal Rye
Crimping cereal rye must be timed exactly to successfully kill the plant and prevent it from going to seed. After stem elongation, it must be crimped several times up and down the stem. The best time to do this is when the rye is in full flower/anthesis (see Figure 6). Do not allow it to grow much past this stage or it could reseed. Crimping is accomplished with a sharp-edged tool such as a shovel. Roller/crimpers pulled behind a tractor are an option for large-scale crimping. Begin by crimping a small area with a light seeding rate (3 oz./100 sq. ft.) and have a backup plan such as glyphosate application, smothering, or pulling if the crimping does not work. Once accomplished successfully, the straw cover offers weed suppression and moisture retention throughout the growing season.
Summary
While there are many considerations for how to use cover crops in the garden, there are also many benefits. Starting small is a great way to learn what works for each garden and gardener. It is important to identify the right combination of benefits offered by a cover crop species and to use the most effective control methods for your garden. Use the proper planting-to-termination strategy to gain soil benefits without losing control of the cover crop. The Midwest Cover Crop Council decision tool at midwestcovercrops.org/selector-tools is designed for row crop farmers but can also offer insight to gardeners.
Resources
To view how different cover crops fare through the winter, check out the Cover Crops at Farm Science Review videos at go.osu.edu/agcropsyoutube.
Additional resources include:
- Planting Cover Crops into Raised Beds, youtu.be/_ldRoQfP5NU.
- Planting Tomatoes into Cereal Rye Residue, youtube.com/watch?v=6mpbflm5RHg.
- Building Soils for Better Crops, sare.org/resources/building-soils-for-better-crops/.
References
Barnes, J. P., & Putnam, A. R. (1983). Rye residues contribute weed suppression in no-tillage cropping systems. Journal of Chemical Ecology, 9(8), 1045–1057.
doi.org/10.1007/BF00982210
Midwest Cover Crops Council, (n.d.). Species. Midwest Cover Crops Council.
midwestcovercrops.org/#
Ozorio, D. V. B., & Basche, A. (2022). How much nitrogen does my cover crop take up and when do I get it back? CropWatch.
cropwatch.unl.edu/2020/how-much-nitrogen-does-my-cover-crop-take-and-when-do-i-get-it-back