Cover Crops Improve Soil Health
By Susy Morris
As gardeners, we know that the success of our edible and ornamental plants is directly related to the health of our soil. Some of us even believe that as gardeners, we nurture and grow soil every bit as much as we do plants. Our soil is one of our most valuable assets, and it needs to be protected. The best way to protect and improve our soil is by keeping it covered with crops, whether that’s crops we’re growing for food or cover crops.
At their most basic level, cover crops are exactly what they sound like: plants that cover the soil and reduce erosion and nutrient loss. Essentially, they are a living mulch.
The first time I used overwintered rye in my garden to prepare a new garden area, I became a believer in the wonderful benefit of using cover crops. I started experimenting with different varieties for different garden areas to mitigate specific issues. I planted daikon radishes to break up compacted soil, crimson clover to add a boost of nitrogen in my vegetable plot, mustard scrubbed my soil of disease before planting potatoes, and my favorite was buckwheat to suppress and control weeds in newly tilled garden areas.
If you have a small garden, you may think that cover crops aren’t for you. Most often, we see them used by farmers on a large scale and think large fields and large tillers and plows are needed. That’s not the case, however. Cover crops can be a valuable addition to your crop rotation schedule in any sized garden, even a square-foot garden.
Cover the basics
In small gardens, cover crops provide the same benefits that they do in a large agricultural setting. Some of their benefits include smothering weeds, mitigating disease and pests, reducing erosion, increasing moisture retention in the soil, enhancing nutrient availability, increasing beneficial micro-organisms, providing forage for animals, adding organic matter, and attracting and providing nectar for pollinators. These wonderful crops can also save the home gardener money by decreasing fertilizer costs and increasing yields. No matter what size garden you have, cover crops are worth adding to your crop rotation schedule.
At the very least, you should be planting a cover crop in your edible garden plot during the fallow season, which is winter in most areas of the country. A fallow season can also constitute 20 to 30 days between crop harvest and planting of the next crop. When utilized during the off-season, cover crops will reduce soil erosion and nutrient loss. By and large, this is their most valuable benefit, especially in our edible garden areas. We work hard to grow our soil, so don’t let the wind blow it away or the rain carry it off. Cover crops are the easiest, cheapest, and most effective way of minimizing soil and nutrient erosion. If chosen properly, a fall-planted cover crop can also provide you with a weed-free planting bed in the spring. That’s definitely something every gardener can get excited about!
Step by step
The first order of business when selecting cover crops is to determine your ability to till or work them into the soil. Do you have a large tiller that can handle large amounts of biomass? Do you have pigs or chickens that can be used to incorporate the crop into the soil? Do you follow a no-till method? Some cover crops can become a problem if you don’t have the necessary equipment to manage them. Overwintered rye is fantastic for reducing erosion, providing biomass, and reducing weed load, but it’s difficult to handle in spring if you don’t have a decent-sized tiller or pigs to incorporate it. A cover crop that winterkills or has shallow roots is much easier to manage if you practice a no-till method.
Second, determine your problem or needs. Are you looking to have a weed-free seedbed in spring? Do you need to increase nitrogen? Do you want to break up compacted soil? Is your soil harboring pathogens or pests? Do you want to attract pollinators? Do you want to add large amounts of biomass? Use these questions as a guide to determine which variety to choose.
Third, identify where, when, and how long you will be using your cover crop. Will you be planting in spring, summer, or fall? Do you only have a one-month window for the crop to grow, or are you planning on using it as an overwintered crop to stabilize soil. What kind of light is available? Is the soil well-drained or waterlogged? Are you under-sowing a growing crop? Just like regular crops, cover crops have water and light preferences as well.
Fourth, settle for the cover crop that best suits your needs – or a rotation of a few to use over a long period of time. Since you won’t be able to find that one-size-fits-all cover crop for your garden, pick the one that best addresses the key benefits you want. Some cover crops can be mixed in order to increase benefits; you can even find premixed cover crops blended for specific purposes. Two of my favorites are the Spring Green and Fall Green manure mixes from Johnny’s Selected Seeds.
Fifth, determine the planting schedule for your cover crops. It’s easiest to start small. Generally, one variety seeded at the end of the gardening season is the best way to get your feet wet. Crimson clover is a particular favorite of mine for this use. As you go through the gardening year, notice fallow times and empty garden areas. These are the ideal times to incorporate quick-growing cover crops like mustard and buckwheat into your current crop rotation. If you don’t plant your cover crop garden until Labor Day, which is a common practice in the Midwest, consider tilling up the garden in spring – hopefully a cover crop was overwintered that can be tilled in – then plant quick-growing mustard to help reduce weed load, keep soil workable, and to disinfect the soil for crops that will follow. If you want a nitrogen-fixer for heavy feeding plants in summer, crimson clover is a great option for early spring planting, as it can take late frosts and cold snaps. If you’re looking to provide valuable nectar for pollinators, choose buckwheat.
Cover crops are grown like most other seed, though spacing isn’t as important when you are using them in the small garden. In fact, I like to plant my cover crops very thickly in order to make sure they are close enough to suppress weeds. Most cover crops will be planted like grass seed. First, work up the soil by loosening the top inch or two. Second, broadcast seed at a medium-to-heavy density. Third, rake into soil and tamp down lightly. I usually walk across the newly planted area to ensure good seed-to-soil contact and help reduce loss of seed to birds. Some seeds, like rye, can be very tasty to birds, especially wild turkeys. Water occasionally, if there is no rain, until you get good germination rates.
Now that your cover crop is planted and has grown, what do you do with it? In many cases, the cover crop is tilled and incorporated into the soil. Generally, this happens about seven to 10 days after flowering, when plants have maximum nutrients, but it can happen at any time after it is established. Even growing mustard, buckwheat, or clover for 2 to 3 weeks will reduce erosion and increase fertility of the soil.
Cover crops can also be crimped over. I sometimes use a 2-by-10 board with a rope on both ends to walk along and fold the crops over – this is a great method when you want to use the cover crop as mulch. If done at the proper time, it will mostly kill the crop. Cutting with a scythe, heavy-duty mower, or hedge trimmers is another option for dealing with cover crops. My favorite way to incorporate rye is to allow our pigs to eat it and root it into the soil. Chickens can also be used for this purpose.
When harvesting cover crops, leave the green growth where it is, or incorporate it into the soil. This will ensure that the nitrogen and other trapped nutrients will be available to future crops. In cases where the cover crop winterkills, there’s no more work on your part, which makes winterkill cover crops a great way to get started into cover cropping. The crop will die when the weather gets cold and will decompose over the winter. You will end up with a wonderfully friable seedbed in spring.
Another consideration when using cover crops is that just about any plant can become a weed if allowed to set seed. For maximum benefits, cover crops should be tilled and worked in right around flowering. Many varieties will set seed and can become weed issues in certain areas. Choose varieties that aren’t aggressive and are easy to manage, like mustard, crimson clover, and buckwheat, if you’re not sure you will incorporate them at the proper time. Even if allowed to set seed, these particular varieties are fairly easy to pull and manage.
After utilizing cover crops in my garden for the past eight years, I have finally found the ones that work best for me. I use mustard, buckwheat and clover most frequently in my established vegetable garden. In newly worked soil that will become garden space, I use a rotation of fall green manure followed by alternating crops of buckwheat and mustard the following summer. In mid-to-late summer, I plant oilseed radish to help loosen the soil deeply. The following spring, my new garden area has beautifully workable soil with very few weeds. Don’t wait! Start using cover crops to reduce your workload and increase the health of your soil this summer. You, too, can save money and time by using cover crops, even if your garden is only a 4-foot-by-10-foot plot.
Choose a Cover Crop for You
There are a wide variety of cover crops used in the large-scale agricultural setting. While just about every single one of these could be used in a home garden, there are a few that stand out above the rest because of their ease of management.
Some cover crops, like sweet clover and vetch, should be avoided because they can become invasive in some areas and are difficult to get rid of once established. Here’s a few I recommend.
Mustard cover crop
This quick-growing plant is at the top of my list when it comes to favorite cover crops to use in a small setting. It not only grows quickly, even in cool spring weather, but it does a fabulous job at disinfecting the soil. Mustard destroys nematodes and fumigates the soil. It has natural biotoxic compounds that work against a wide variety of bacteria, nematodes, fungi, weeds and insects. Brassicas are especially beneficial at scrubbing the soil of disease to make way for potatoes as they inhibit the potato-root eelworm.
Buckwheat (Fagopyrum esculentum) cover crop
This summer annual (non-legume) is very effective at suppressing weeds because of its quick growth. Plant thickly for maximum weed suppression. It also supports beneficial insects with habitat and food. In addition, it helps loosen topsoil and rejuvenates soil because it breaks down quickly and thrives in low-fertility soils. It thrives in cool, moist conditions, thus it is not as useful for those in hot, dry climates.
Oilseed radish cover crop
With its very large taproot that can reach up to 6 feet deep, this is a star at breaking up hardpan soil and increasing water absorption in compacted soil. This deep taproot harvests nutrients from deep down and makes them available for the crops following it. As a fast-growing cover crop, even in cool seasons, oilseed radish can be used when crops are harvested late.
Crimson clover cover crop
As a legume, crimson clover provides a valuable nitrogen source for the crops that follow. It is especially useful when overwintered as a nitrogen source for early planted brassicas that are heavy feeders. It’s a fast-growing plant that will quickly cover the ground and suppress weeds very well, which makes it beneficial during short breaks in between harvest and replanting. Crimson clover is a stunning cover when in bloom – the pollinators come in droves. In colder climates, crimson clover will winterkill and provide a nearly weed-free seedbed in spring.
Winter rye cover crop
This is perhaps one of the best cover crops if you have a way to incorporate it into the soil (pigs do a great job of this). It is one of the best cover crops to use on new garden areas, as it thrives in poor, dry and sandy soils. It also does not need soil to be prepared meticulously, which makes it a valuable first round of cover crop on newly broken ground. Rye suppresses weeds because it is allelopathic (meaning it discourages neighboring seeds from germinating). It’s helpful at reducing nematodes and soil-borne diseases, and is quite beneficial at scavenging nitrogen and holding it over the winter. Since rye is a grass, it does support cutworms and wire worms. It should not be used in areas where potatoes and other grassy plants will be grown the following season. Rye is beneficial for those living in cold northern climates – it can be seeded very late in the season.
Susy Morris is a Maine-based blogger, photographer and small-scale farmer who loves to try new things and experiment with different techniques to make her farm and garden more sustainable.
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