Leaving garden soil bare can contribute to erosion and the release of carbon into the atmosphere, but planting cover crops can do a lot of good.
After harvesting the last few beans, tomatoes and peppers, I usually just yank the plants, rake up the debris, and toss it all in my super-hot compost pile. As for my garden beds? They remain mostly bare until spring.
I’d always assumed cover crops were for large-scale farmers or people who grew heavy feeders like corn. But the increasing numbers of extreme weather events and the current climate crisis we’re all facing have changed my mind.
Cover crops afford all sorts of benefits—even for small-time growers like me. They prevent soil erosion and crowd out weeds. Cover crops also boost soil fertility, help to conserve moisture and improve the soil’s overall structure.
So, even for my relatively small garden plots, I now see value in planting both green manure—crops like peas or buckwheat planted during the regular growing season—and more traditional cover crops like winter rye.
And especially important now? By covering the soil with certain types of plants—whether between successive plantings of crops or between entire growing seasons—we can trap carbon. Sequestering carbon in the soil can keep it from escaping into the atmosphere.
And keeping rogue carbon in check can help to mitigate the planet’s rising temperatures.
Read More: PEST CONTROL AND MANAGEMENT
Room to Rotate?
Green manures and cover crops can also help growers with little-to-no ability to leave plots of land fallow.
“If you grow intensively in order to cram a lot of production into a small space year after year after year, your soil health and fertility are going to go down,” Certified Organic Inspector Gary Ogle explains. “So, if you have enough land that you can always practice good crop rotation—which not only increases soil health but also resists disease and pests—then you are off to a really good start.”
But if you don’t have acres and acres of land at your disposal?
“Taking the time to plant green manures—even though you might be using [part of] your land to grow something you’re not going to sell and you may just end up tilling under—you’ve got to remember that you’re growing that crop in order to build your soil tilth,” Ogle says.
“That’s going to give you a better crop the following year. It’s an investment. It can be a challenge for many people, but it’s definitely worthwhile.”
Mix and Match
Ogle also works on seed variety selection and catalogue production for Veseys in Canada’s Atlantic region.
“On our own trial farm, we’ll grow an early crop of buckwheat just to break up the soil and to control weeds,” he says. “Often we will follow that up in September with a crop of winter rye, so we have something green holding the soil in the winter.”
“In other areas, we’ll often put in our own custom mix,” Ogle continues. “We’ll put in beans and peas and other legumes, such as alfalfa and clover, and we’ll till that in.”
Depending on your soil’s specific needs, you can customize your own cover crop mix, too. Field peas, hairy vetch, and white clover expertly fix nitrogen in the soil. Crops like mustard and radishes will help break up heavily compacted areas.
Still other crops—think crimson clover (Trifolium incarnatum)—provide extra forage for pollinators.
Cornell University developed this online tool with New York-based growers in mind. Still, it could be useful if you live in a similar climate zone or you simply want to identify potential cover crops according to different soil management goals.
Don’t want to make your own mix? Some pre-mixed cover crops like “Protect & Fertilize Green Cover Crop Blend” are commercially available. Containing winter rye, hairy vetch, daikon radish, rapeseed, purple top turnip and Austrian winter peas, the Rene’s Garden mix covers 500 square feet.
Read More: GREENHOUSE FARMING
Many cover crop-related resources mention the need for mowing and tilling—first to prepare the bed for planting and, later, for working the cover crop vegetation back into the soil. Rather than break out my carbon-emitting, gas-powered gadgets to prepare the areas to be planted, I’ve instead covered the spaces with cardboard.
In a week or two, the cardboard will smother any vegetation below. Then I can rake the soil and direct-sow my cover crops. I’ll keep the seeded beds moist until the new crops are established.
Then, in early spring, I’ll cut it down either with my reel mower or scythe. Finally, I can let the spent vegetation serve as mulch above ground or hand-dig it back into the soil a month or so before planting my early spring garden.
Types of Cover Crops
Many types of plants can be used as cover crops. Legumes and grasses (including cereals) are the most extensively used, but there is increasing interest in brassicas (such as rape, mustard, and forage radish) and continued interest in others, such as buckwheat. Some of the most important cover crops are discussed below.
Leguminous crops are often very good cover crops. Summer annual legumes, usually grown only during the summer, include soybeans, peas, and beans. Types of legumes are Kidney beans, maize, lentils, and peas. Soybeans, chickpeas, lupin are less popular but are still very useful.
Commonly used grass cover crops include the annual cereals (rye, wheat, barley, oats), annual or perennial forage grasses such as ryegrass and warm-season grasses such as sorghum-sudangrass. Nonlegume cover crops, which are mainly grass species, are very useful for scavenging nutrients—especially N—leftover from a previous crop. They tend to have extensive root systems, and some establish rapidly and can greatly reduce erosion. In addition, they can produce large amounts of residue and, therefore, help add organic matter to the soil. They also can help suppress weed germination and growth.
It will grow better than many other cover crops on low-fertility soils. It also grows rapidly and completes its life cycle quickly, taking around six weeks from planting into a warm soil until the early flowering stage. Buckwheat can grow more than 2 feet tall in the month following planting. It competes well with weeds because it grows so fast and, therefore, is used to suppress weeds following an early spring vegetable crop.
Used as cover crops include mustard, rapeseed, and forage radish. They are increasingly used as winter or rotational cover crops in vegetable and speciality crop production, such as potatoes and tree fruits. Canola grows well under the moist and cool conditions of late fall when other kinds of plants are going dormant for winter. Example of Brassicas are:
- Broccoli and Calabrese.
- Brussels Sprouts.
- Choy Sum/ Chinese cabbages.
- Certain Mustards.