This is the first of a monthly series on cover crops, which will take us through a whole year, to April 2024.
Why Grow Cover Crops?
<a title=”USDA, Public domain, via Wikimedia Commons” href=”https://commons.wikimedia.org/wiki/File:Soil_food_webUSDA.jpg”><img width=”512″ alt=”Soil food webUSDA” src=”https://upload.wikimedia.org/wikipedia/commons/thumb/8/89/Soil_food_webUSDA.jpg/512px-Soil_food_webUSDA.jpg”></a>
See my post Cover Crops in Summer.
- Cover crops suppress weeds and provide a boost to soil organic matter.
- Keep live roots in the ground as much of the time as possible, to feed the microorganisms in the Soil Food Web.
- Here is a diagram of the Soil Food Web: https://upload.wikimedia.org/wikipedia/commons/8/89/Soil_food_webUSDA.jpg
- Roots anchor the soil, preventing erosion in heavy rains.
- Dead roots also have a role, providing drainage channels in the soil and letting air in deeper.
- Adding organic matter to the soil is a way of sequestering carbon, as well as providing nutrients for your crops.
- Deep-rooted cover crops draw up nutrients, bringing them up where crop plants can access them.
- Leguminous cover crops provide nitrogen, saving imports of organic fertilizers or a big compost-making operation.
- Too often, gardeners grow cover crop only in the off-season, to protect the soil in winter, and assume it’s not a summer option. But it is, and planting summer cover crops provides many benefits.
Focus Cover Crop for May: Buckwheat
I have a blog post Buckwheat, a wonderful summer cover crop, introducing an article I wrote for Growing for Market magazine. See that post for basic details I mostly won’t repeat here.
Buckwheat (Fagopyron esculentum) is a fast-growing warm-season broadleaf annual that is a very useful cover crop. Its special strengths are in weed-suppression, attracting beneficial insects, improving the soil tilth (aggregate structure) with its fibrous roots, and extracting potassium, calcium and phosphorus from the soil to the benefit of following crops. Buckwheat is almost three times as good as barley in scavenging phosphorus, and more than ten times better than rye (a poor phosphorus scavenger). Because buckwheat is not related to any of the common food crops, it is simple to include in rotations.
Buckwheat can be sown up from your last frost up to 35 days before first fall frost. Buckwheat can close its canopy in just two weeks, preventing the soil baking in summer conditions. Because it matures quickly, and self-sows, it can be used in several successions with tilling between, to suppress some perennial weeds.
Buckwheat can do fairly well on poor soils, is tolerant of a range of soil pH and is an easy crop to deal with manually or with small-scale equipment. Even mature buckwheat plants are easy to deal with using manual or small-scale equipment. You can just pull up the plants by hand, or use a hoe or scythe to slice them off at the soil line. You can chop them into the soil, or gather them up and compost them. Or you can use a no-till method, let the dead plants die into a surface mulch and plant through them.
Buckwheat yields only a couple of tons per acre, but does it in only six to eight weeks. If you want to increase the (admittedly sparse) biomass, cut down buckwheat just before it reaches 25% bloom, to a height above the lowest leaf node. Buckwheat will regrow rapidly and you may even be able to make a second cutting.
Buckwheat also makes good food for poultry or rabbits, and chickens love the seeds. It does not provide good forage for larger livestock.
Barbara Pleasant, in her 2009 article Cover Crops, described Rhizodeposition as a special advantage of using cover crops. Many plants release sugars and other substances through their root hairs into the soil. They are solar-powered pumps, sending energy down into the soil, causing the root tips to host colonies of useful microorganisms. As the roots move deeper, the microbes follow. With vigorous winter cover crop plants, like oats or rye, this process goes on down to 6 feet (much more deeply than you should dig). Buckwheat doesn’t go very deeply at all, but it can be working for you, which is much better than leaving the soil empty and drying out.
- e-Organic: Buckwheat for Cover Cropping in Organic Farming and a video clip
- Mark Schonbeck, Principles of Sustainable Weed Management in Organic Cropping Systems
- Mark Schonbeck and Ron Morse, Virginia Association for Biological Farming, Seeders: Using Manually-operated Seeders for Precision Cover Crop Plantings,
- Country Living How to De-hull Buckwheat with the Country Living Mill
- Harvey Ussery, The Modern Homestead, Four Outstanding Cover Crops for Summer
- Cornell Buckwheat Cover Crop Handbook (thorough, but not organic) .
Secondary Cover Crops for May
Soy, mustard, sunn hemp, southern peas are all also good summer cover crops, and I will say more about them in the next few months. See Cover Crops in Summer.
Sunn hemp, a nitrogen-fixing legume from the tropics, can grow as tall as 9’ (2.7 m) in a few months. Sow sunn hemp from a week after your sweet corn sowing date, up to 9 weeks before your first fall frost, which will kill it. It tolerates a wide range of soils (but not if waterlogged). Plant inoculated seed (use the same inoculant as for southern peas) 1” (2.5 cm) deep, with seeds 1.5” (4 cm) apart in the row, and with rows 6” (15 cm) apart. Sowing densely (as with all cover crops) will work better to smother the weeds.
If you sow sunn hemp in a summer gap between spring and fall vegetable crops, it will provide a nitrogen boost for the fall crop, because it is a legume. In dense plantings, it can fix more than 120 lbs (54 kg) of nitrogen and 12 pounds of biomass per 100 sq ft (0.56 kg/sq m). 60 days after sowing, the stems thicken and become fibrous and high in cellulose; cutting at this stage produces long-lasting mulches that increase soil carbon. If you cut the crop back at a younger stage, this will stimulate branching (more biomass) and more root penetration (better drainage).
We have taken to sowing sunn hemp as a summer cover crop in our hoophouse, and lopping it periodically with hedge shears to an ergonomic elbow height. This is because we don’t want it to shade crop plants further back (north). The fallen tops make a nice “forest floor” carbonaceous mulch.
Mustard we don’t grow as cover crops, although I do have experience of growing it in England, where it is one of the favorite cover crops for short crop gaps, or in preparing areas reclaimed from pasture or lawn. We have too many harlequin bugs, and we hope to break their lifecycle by having a summer month without any visible brassicas. (We do often have fall brassica seedlings growing under insect netting.) Also, our “crop portfolio” has plenty of brassicas already, and we’d rather have a better rotation, with brassicas less often.
Mustards can decrease weeds, or certain pest nematodes, if you grow the right kind.
Soybeans are a great summer cover crop and they are also a legume, so they add nitrogen to the soil. They have good shade tolerance and tolerance to foot traffic (that is, people harvesting crops on either side. Because of this, we like using soy to undersow in sweet corn.
Southern peas are another warm weather cover crop option. They are also a legume, and so will add nitrogen to the soil. Iron and Clay is the sprawl variety best known for cover crop use, but other varieties also work.
Cover Crop Planning
My book Sustainable Market Farming has a chapter on cover crops and 9 pages of charts about particular options.
The book Managing Cover Crops Profitably (third edition) from the Sustainable Agriculture Research & Education Program (SARE), is the best book I know on the subject. You buy the book for $19 or download it as a free PDF from SARE.
See Harvey Ussery Four Outstanding Cover Crops for Summer.