Growing cover crops is a great way to protect and build garden soil in the off-season when your beds aren’t hosting summer veggies and flowers. Below, I’ll go over the basics of cover cropping in gardens and 9 of the best winter cover crops for gardens to get you started.
A cover crop can be any crop grown primarily to build soil rather than to harvest. A lot of research and information exists on the use of cover crops in farming, but it’s a lot to wade through. And it’s hard to know what information applies to cover cropping in small backyard gardens.
In this post, I’ll go over the many benefits of planting cover crops in your garden. I’ll also help you choose the right winter cover crops for your situation, and explain how to manage them in gardens.
The Many Ways Cover Crops Improve Garden Health
Weed Control
Cover crops grow quickly, outcompeting many weeds for light, water, and nutrients. This method, specifically known as “smother cropping,” can, in some cases, completely smother out weeds. In other cases, cover crops can control weeds to a manageable level.
Pest and Disease Control
Rotating crops with cover crops can control pests and diseases by removing the host plant and replacing it with a cover crop that does not support the pest. Cover crops also increase the biodiversity of a garden, both above and below ground, which naturally reduces pest and disease problems.
Certain cover crops, such as brassicas, also contain compounds that can help control plant diseases.
Diversify Soil Life
The organic matter left by cover crops feeds soil microorganisms and earthworms, causing a bump in the population of countless beneficial critters.
Improve Soil Physical Properties
Cover crop roots penetrate the soil, reducing compaction and leaving organic matter behind when they decompose. This improves the soil’s structure, aeration, and water-holding capacity.
Add Fertility
Some cover crops (mainly legumes) fix nitrogen from the air and store it in root nodules for the plant to feed on. When the plant dies, its nitrogen-rich leaves release that nitrogen into the soil.
Other cover crops accumulate nutrients including nitrogen, phosphorus, potassium, and micronutrients from deep within the soil. These are incorporated into the top few inches of soil as the biomass decomposes.
Additionally, the humus-rich material created from decayed cover crop biomass holds onto nutrients, keeping them from leaching out of the soil.
Attract Beneficial Insects
Winter cover crops provide late-season pollinators and beneficial insects with both food and habitat into the colder months when resources might otherwise be scarce.
Prevent Soil Erosion
The roots of cover crops hold the soil together and the foliage covers the soil, protecting it from winds and exposure that can erode topsoil.
The Two Main Types of Cover Crops
The two main categories of winter cover crops are winterkill and winter hardy.
Winterkill cover crops are planted in late summer or early fall and don’t survive winter freezes. They don’t grow as much biomass as winter hardy cover crops do, but because they die over winter, they are easy to manage and beds are ready for planting in early spring.
Winter hardy cover crops overwinter, with vigorous growth the following spring. They provide more biomass, but also require more time to grow in spring and are more work than winterkill cover crops. They should be terminated after flowering but before going to seed.
Winterkill Cover Crops
Here are some of the best winterkill cover crops for gardens. Note that, depending on climate, some of these may overwinter and should be mowed or cut down in spring before going to seed.
Winter Hardy Cover Crops
Following are some of the best winter hardy cover crops for gardens. In cold climates, some of these, such as crimson clover and annual ryegrass, may winterkill.
Killing Garden Cover Crops in Spring
If cover crops are not killed or they are killed too late, they’ll drop seeds, which might be a nuisance in the garden. If they’re cut too early, the plants could regrow and produce seeds later in the season.
On farms, heavy equipment is used to roll, crimp, or mow cover crops in spring. Even market gardens use large crimpers to flatten and kill crops, but this equipment isn’t practical for a backyard garden. Often, pesticides are used to kill cover crops, but I don’t recommend that.
Better tools exist for the home garden. Below are some smaller-scale options for terminating cover crops.
- Cut them at the base with garden shears, a scythe, or a weedwhacker.
- Mow them with a mulching lawn mower.
- Cover the beds with black plastic for a week or two.
Cover Crop Mixes
Often cover crops are sold as mixes that compliment each other. You can also create your own mixes. Here are some standard mixes, but see the table below for more mixing options.
A Good Winterkill Mix
A common cover crop combination is field peas and oats. Oats grow quickly into tall stalks and suppress weeds. Field peas fix nitrogen and want something to climb, making them complement each other well. Plus, both die off with winter freezes in zone 6 or 7 and below.
Forage radish is a good third crop to mix into this blend. The deep taproots break up compacted soil and when the plants die in winter, the roots and foliage leave behind organic material that mulches and supplies nutrients in early spring.
A Good Winter Hardy Mix
A common winter hardy cover crop combination is winter rye and hairy vetch or crimson clover, or all three. Rye grows a lot of biomass, suppresses weeds, and increases soil organic matter. Crimson clover and hairy vetch both fix nitrogen and attract beneficial insects. Both also tolerate some shade, so do well under the taller rye.
Winter Cover Crops for Gardens
Cover Crop | When to Sow | Winterkill in Zones… | Main Benefits | Mix With | Notes |
|---|---|---|---|---|---|
Field Pea | 6-8 weeks before first frost date | 7 and below | fixes nitrogen (legume) | wheat, rye, triticale, or barley for vertical support | climbing vines |
Oats | 6-8 weeks before first frost date | 6 (and usually 7) and below | quick growth, add organic matter, suppress weeds | clover, pea, vetch | a.k.a spring oats |
Forage Radish | August | 8 and below | reduce soil compaction, aerate the soil | field pea, oat | a.k.a. daikon radish, tillage radish |
Arugula | August | 8 and below | reduce soil compaction, suppress weeds | Other brassicas or mustards, small grains or crimson clover | don’t rotate with other brassicas |
4-6 weeks before first frost | 7/8 and below | excellent nitrogen fixer (legume), breaks up clay and compacted soil | oats, forage radish | People deficient in an enzyme (G6PD) shouldn’t handle seeds, consume fava beans, or inhale its pollen. | |
6-8 weeks before first frost | 5 and below | fixes nitrogen (legume), attracts beneficial insects, and fast-growing | Rye, vetch, and other clovers | tolerates some shade | |
Annual Ryegrass | At least 40 days before first frost date | 5 and below | prevent erosion, improve soil structure and drainage, add organic matter, suppress weeds, scavenge nutrients | field pea, fava bean, other grasses | quick-growing, non-spreading bunch grass |
4-6 weeks before first frost date | 4 and below | fixes nitrogen (legume) | rye, field peas, crimson clover | tolerates some shade | |
Winter Rye | Early Fall | 3 and below | scavenge excess nitrogen, prevent erosion, add organic matter, suppress weeds | crimson clover, hairy vetch | a.k.a cereal rye; winter wheat and barley are similar |
Steps For Cover Cropping Your Garden
1. Choose your cover crop or mix
The information above and the table below will help you decide on the best cover crop for your needs. Also, consider what you have planted before and will be planting after.
- If your main crop is still growing into the fall, you’ll need to choose winter hardy cover crops that can be planted later in the fall.
- If you’re planting early spring crops, you’ll need to choose a winterkill cover crop in order to start the cooler weather main crops early enough.
- Avoid planting the same family for both main and cover crops. For example, Arugula or mustards should not be planted as a cover crop before the main crop of other brassicas such as kale, broccoli, or kohlrabi.
2. Sow and care for your cover crop
- Remove any mulch or residue of the prior harvest from the garden and rake the surface to create an even seedbed for sowing.
- Broadcast the seeds evenly over the surface, gently rake them in, and water them.
- Depending on the crop, you can add a thin layer of fine mulch back to the bed after sowing.
- Cover the seeds with a floating row cover or old bed sheet to protect them from becoming bird food.
- When seedlings begin lifting the cover, remove the cover.
- In very dry climates keep the bed watered as necessary until the first hard freeze or snow.
3. In spring, kill cover crops that didn’t die over winter
- Timing is important to ensure an effective kill. Wait for blooms to emerge, but cut before seeds form.
- Use garden shears or another cutting method to cut down crops, or cover them with black plastic or landscape fabric.
- Leave the cut plant material in place to mulch and replenish the soil.
4. Plant your main crop in the residual mulch
- For winterkill cover crops, seeds can be sown in early spring. For Overwinter cover crops, you’ll have to wait until they reach maturity and are killed.
- You can dig the mulch into the soil, or leave it in place on top for no-dig gardens.
- If you choose to dig the mulch in, wait two to three weeks after digging before planting or sowing.
- For no-dig gardens, make small holes in the mulch and transplant seedlings into the soil beneath. Large seeds can be pushed into the soil through the mulch.
- For smaller seeds in no-dig beds, clear a narrow row to plant into. A hoe dag might be useful for creating a furrow in mowed beds.
What About Eating Cover Crops?
It’s tempting to grow cover crops that are also edible so that you can continue to grow and eat from your garden throughout the year.
Although this is definitely possible, and many people do it, be aware of the trade-off. When you harvest your cover crop, all of those nutrients go into human food rather than feeding the soil. That said, you can certainly find a happy medium, yielding a small harvest, and still leaving plenty of plant material behind to work its magic on the garden soil.
Also, be aware that most seeds advertised as cover crops are selected for that purpose, not necessarily for consumption. Though they may still be edible, they aren’t selected for their palatability.
Conclusion
For the healthiest gardens, never leave your garden beds bare. The best time to prep your garden for spring is in the fall. At the very least, top them up with mulch, but better yet, grow some cover crops.
So get some cover crop seeds and get sowing. And check out the references below for more information.
Happy cover-cropping!
References
- Botanical Interests, Cover Crops for a Naturally Better Garden
- Botanical Interests, Cover Crops – Growing Soil Health!
- Sustainable Agriculture Resource and Education (SARE) Managing Cover Crops Profitably
- eOrganic YouTube Video Using Winterkilled Cover Crops to Facilitate Organic, No-Till Vegetable Planting
- Sustainable Market Farming, Winter Kill Temperatures of Winter-Hardy Vegetables
- Botanical Interest USDA, Plant Hardiness Zone Map
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