Are you looking to improve the health of your soil and the health of your garden ecosystem overall? Then cover crops may be the solution you’ve been searching for! Cover crops for raised beds are particularly useful. Raised beds can lose soil structure, becoming compact over time. They can also lose nutrients over time without any supplements such as added, organic matter like compost or the use of fertilizers, etc. There is an option that is even better and it is known as green manure or, in other words, cover crops! There are many choices of cover crops for raised beds from leguminous crops with their nitrogen-fixing nodules to flowering cover crops like alfalfa that attract pollinators and other beneficial insects to your home vegetable garden.
The benefits of planting cover crops include, but are not limited to the following: providing a living type of mulch, increasing soil health, acting as a weed suppressant, improving soil structure, and heightening soil decompaction and aeration. Many different plants can be used as cover crops, but the best cover crops will be fast-growing plants. Look for crops to plant that grow quickly within their first few weeks, like crimson clover or legumes, and that are easy to terminate. This will allow you to improve your garden soil quickly and then continue growing vegetables and/or flowers in your raised bed.
It may seem like additional work, but because these crops grow so quickly and because generally, you aren’t using them for food (although some are also edible!) they don’t require a lot of extra care. The cover crop seeds don’t need to be painstakingly spaced. Especially if you aren’t growing the plants to full maturity, then just evenly broadcast a layer of seeds over the soil, lightly rake them in, or dust with some soil over top, and you’re done planting cover crops in your raised bed! Keep them well watered and moist until they germinate then water deeply at least once a week or more often during dry periods. Some winter cover crops require little to no water at all. They will receive all the moisture that they need from winter snowfall.
There are many different types of cover crops to choose from, but fear not! You don’t need to pick just one. Several seed companies sell cover crop seed mixes that contain a blend of 8-9 of the plants that we’ll discuss here so that you can reap a variety of benefits.
Why Should You Plant Cover Crops?
As mentioned above there are many reasons to plant cover crops in your raised beds. In addition to overall soil improvement, the moisture retention of your raised bed is also improved, the organic content of the soil improves by increasing the amount of biomass both above and below the ground, compaction is reduced, earthworms and other beneficial insects are attracted and given habitat to remain in your garden as well. Most interestingly, some cover crops are expert suppressants of weeds because they are allelopathic. Allelopathic plants can prevent weed seeds from germinating by releasing biochemicals also referred to as allelochemicals.
Planting cover crops is a form of crop rotation that allows a cover crop to take the place of what you had been growing and rotating in before you go back to growing those vegetables again. Not only that, but you reduce the risk of erosion or loss of nutrients in bare soil that can occur when you haven’t been planting something to cover it up. Planting a fast growing crop is a lifesaver in so many different ways!
Types Of Cover Crops For Raised Beds
Below we’ll discuss the most common types of cover crops and why they will be beneficial for your raised bed. There are cool-season cover crops that prefer to be planted in early spring, early fall cover crops, winter cover crops, and even perennial cover crops. The best cover crops will add plenty of organic matter to your raised bed soil which in turn will reduce soil erosion and soil compaction. Most cover crops provide dense cover which helps with weed control. There are edible crops that can be used in this way as well. They can be harvested at an immature stage or grown through to maturity.
There are four main types of cover crops to choose from: grasses, legumes, brassicas, and broadleaf plants. Generally speaking, you will plant these cover crops 4 weeks before your first frost date in the fall unless otherwise noted. They will be left in the soil over winter to protect it from the elements. When you grow cover crops, they can be used throughout the year in between plantings of vegetables or alongside them to help crowd out and prevent weeds.
Buckwheat is the fastest-growing cover crop and because it grows so quickly, it can be grown at virtually any point in the growing season. It is also an example of a cover crop that induces the above-mentioned allelopathic effect, making it a great choice for your raised bed if weed suppression is your goal. It is edible and can be grown for its microgreens, or left to mature and you can harvest the seeds which are used to make flours. However, it’s important to note that generally cover crops aren’t grown to maturity because then they end up taking nutrients from the soil to mature rather than adding nutrients to the soil. Buckwheat is often grown in the late summer or as a fall cover crop. It is extremely frost sensitive and will die after a frost. You can leave the frost-killed buckwheat in place to reap the benefits of it as a living mulch as well.
Learn More: Buckwheat Plant
Alfalfa is a perennial cover crop in the pea family that is known to fix nitrogen into the soil. It’s best to plant it following crops that depleted nitrogen from the soil, such as corn. It is commonly grown as forage for farm animals because it contains high amounts of protein. It will also produce stunning purple/blue flowers that will provide much-needed food for pollinators as well. This cover crop is very easy to chop and drop and utilize in the same way you would straw mulch. Cut foliage back to the soil level and simply drop the greens onto the soil. Allow them to dry out and break down over the winter. Then come spring, plant your next crop as your normally would.
Learn More: Growing Alfalfa
Where to begin! There are many many many types of clover, not just the common 4 leaf variety! And most of them can be used as cover crops in raised beds. A few popular types include white clover, red clover, and crimson clover. Clover is related to other legumes such as peas, beans, and peanuts. As with other plants in the legume family, they fix nitrogen into the soil via nodules that grow along the roots. Clover establishes itself in early spring and has a spreading growth habit which makes it an excellent weed suppressant. It will produce flowers for the bees and beneficial insects as well – particularly crimson clover, as it is often one of the first flowers to burst into bloom among spring crops.
Learn More: Clover Cover Crops
If you’re looking to add a large amount of biomass and organic matter to your soil then look no further than rye. Most commonly cereal rye, such as winter rye is used as a cover crop. Winter cover crops like winter rye have fibrous roots that add plenty of biomass below the soil when allowed to decompose in place. It won’t necessarily die on its own over the winter as it can be extremely frost-hardy. Therefore, you may need to kill it to turn it into a hearty mulch. Winter rye can be terminated by mowing it, using the chop and drop method, or even smothering it with a tarp.
Oats are another member of the grass family, like rye, that can be grown over winter and into the spring. This is a great option for home gardeners who live in a temperate climate with a shorter growing season. Oats can be sown in fall and grown over winter or they can be sown in spring and grown into the late summer.
Learn More: Growing Oats
Hairy vetch, like rye and oats, can survive over winter in most areas and are best used as a mulch. It is a great choice for improving sandy soil. It will help increase moisture retention and prevent further soil erosion. This winter cover crop is also a legume that will fix nitrogen into the soil. Hairy vetch produces beautiful small purple flowers as well. Vetch also has a spreading growth habit that makes it a great ground cover. It can be viewed as invasive because of how quickly it spreads along the ground, but it is easily controlled and usually doesn’t affect healthy native plants.
Sorghum, or sudangrass, makes an excellent winter mulch to protect your soil from harsh elements or from weeds. It has an extensive root system which adds an abundant amount of organic matter to your soil. Sow sorghum in mid-fall and either mow it down after a few weeks of growth or allow the winter frosts to cause it to die back.
Learn More: Sorghum Plant
There are many types of millet, but most commonly pearl millet is used as a cover crop and it is generally not sown on its own, but rather as a part of a mix of cover crop seeds. Millet has many special benefits including being very heat tolerant to hot and dry conditions. It can also tolerate sandy soil. Like most members of the grass family, millet can readily self-seed for the next year and restart its life cycle. When utilizing this plant as a cover crop be sure to cut it back before it goes to seed unless you want it to spread.
Learn More: Millet Plant
Also known as field peas, or more commonly known as black-eyed peas. They have a long taproot which makes them a great choice if your goal is to prevent soil erosion. They are heat and drought-tolerant which also makes them a good choice for home gardeners in warmer climates. Cowpeas will add nitrogen to the soil and are also edible should you choose to grow them to maturity.
Unlike cowpeas, regular peas do not tolerate heat/drought and are most definitely considered cool-season cover crops. Another member of the legume family, peas also have nitrogen-fixing properties. Peas are frost-hardy and can be grown later into the season in temperate climates. They can be left in place as mulch, or harvested as edible young pea shoots.
Learn More: How To Grow Peas
Lentils are a great cover crop choice in cooler seasons since they are very cold tolerant although they cannot survive below-freezing temperatures. Lentil seeds will germinate at 40 degrees Fahrenheit. They are a winter annual legume that provides excellent ground cover. Cover crop plants in the lentil family can survive in low moisture environments as well.
Learn More: Growing Lentils
Mustard is a great choice for home vegetable gardens that may be struggling with pests and diseases in their raised bed soil. Mustard contains high levels of glucosinolates which are known to suppress soil-borne fungi and even nematodes. Plus, mustard greens are edible and quite delicious! They also have extremely long taproots which can extend 3 feet below the soil which will greatly improve your soil structure. Be forewarned that when mustard goes to seed, it will readily self-seed the area and you might find “mustard weeds” popping up later, but that just gives you more salad components to make use of!
Learn More: Growing Mustard Greens
Although barley is less winter hardy than rye, it can be grown through the winter months in mild climates such as zone 8 and above. As with many of the other grasses mentioned above, barley also has a deep and fibrous root system which adds a wealth of organic matter to the soil. It can easily be mowed down and left in place as a mulch.
Learn More: Growing Barley
Winter wheat, just ahead of oats and rye, is the most common choice for a cover crop. It germinates readily, grows very quickly and it’s easy to plant in fall and then wait for the winter frost to kill it back for you. For these reasons, this is a great choice for those just beginning to learn to grow cover crops.
Learn More: Growing Wheat
There are two main types of radishes that are used as cover crops: oilseed and daikon. Oilseed radishes will grow faster than daikon since the roots don’t grow as thick. Oilseed radishes are technically edible but are not usually grown for culinary use. Since the oilseed roots don’t grow as thick this allows the plant to focus on the foliage which will provide you with plenty of green manure to feed your soil microbes. The roots can also be left in place to decompose in the soil quicker than the thicker root of the daikon radish.
Daikon radishes, however, are a good choice if you’d also like to get an edible harvest from the cover crop you planted. These root vegetables are also a good choice if your goal is to aerate compacted soil.
Learn More: Growing Daikon Radish
Triticale is a mix between wheat and cereal rye and because of this, it shares many of the same properties as the above-mentioned plants. Growing these cover crops in raised beds will prevent weed growth and if you choose to forgo using them as mulch they also make an excellent addition to the compost pile.
Also known as chickpeas, these summer crops are generally planted in early spring and harvested in late summer. A spring planting of garbanzo beans is often used in crop rotation between wheat and barley to help break the cycles of pests and diseases shared by those two plants.
Learn More: How To Grow Chickpeas
Scarlet Runner Beans
These are a perennial cover crop in mild climates like zone 7 and above otherwise they are grown as an annual. Scarlet runner beans are also edible but must be cooked first. They will add nitrogen to your soil and provide beautiful red flowers for the pollinators in your garden. Fava beans also have many of the same specific benefits!
Frequently Asked Questions
Q: What is the fastest-growing cover crop?
A: Buckwheat is the fastest-growing cover crop that can grow 2-3 feet within 4 weeks.
Q: What is a good cover crop for a vegetable garden?
A: Ryegrass, hairy vetch, and clover are all good choices of cover crops for a vegetable garden. All of these crops grow quickly and have a large root system that adds biomass below the soil as well as above it.
Q: When should you plant cover crops?
A: A general rule of thumb is in the fall, one month before your first frost date, but they can be planted at any time of the year to protect bare soil.
Q: What is a no-till cover crop?
A: This usually refers to the chop and drop method of cover cropping which calls for the crops to be cut down at ground level. The roots are left in the soil to decompose and the above-ground foliage is dropped in place to die back and create a mulch for the raised bed.