At the end of a growing season, a vegetable bed can look tired.
The last tomatoes are gone, the beans are pulled, and the soil sits bare.
Bare soil is not really resting, though.
Rain packs it down and washes it away, and weeds move in quickly.
A cover crop is a calm way to protect that soil until you plant again.
It is a crop you grow for the soil, not for the kitchen.
You sow it, let it grow, and then return it to the ground.
This guide follows the cover crops fact sheet from Clemson Cooperative Extension.
What a Cover Crop Does
Clemson Extension lists five main reasons to plant one:
- It protects the soil from erosion.
- It suppresses weeds.
- It helps the soil hold moisture.
- It adds organic matter.
- It recycles soil nutrients.
Cover crops are sometimes called green manures.
They are not harvested.
Instead, they improve the soil right where they grow.
Clemson Extension notes that most gardens benefit from cover crops instead of sitting unplanted.
The Two Main Groups
Legumes
Legumes include clovers, vetch, peas, cowpeas, and soybeans.
With help from soil bacteria, they take nitrogen from the air and store it in their roots.
When the plants are cut and break down, some of that nitrogen becomes available to the next crop.
Clemson Extension advises treating legume seed with the right inoculant at planting.
The inoculant supplies the specific bacteria that help the roots fix nitrogen.
Without it, nitrogen fixation will be low.
Cover crops will not supply all the nitrogen the next crop needs.
Over the years, though, they help build better soil.
Non-legumes
Non-legumes are mostly grains, such as oats, cereal rye, barley, and wheat.
Buckwheat and some brassicas, like mustard and daikon radish, belong here too.
Their main gift is biomass, the stems, leaves, and roots that become organic matter.
That organic matter improves soil structure and helps it hold water.
It also feeds the helpful microbes that live in the soil.
Mixing the Two
Clemson Extension prefers a mix of a legume and a non-legume for most gardens.
The legume adds nitrogen, and the grain adds plenty of organic matter.
A popular fall and winter mix is crimson clover with cereal rye.
A common summer mix is cowpeas with buckwheat.
Many seed catalogs sell ready-made mixes.
To make your own, use the lower seeding rate for each crop in the mix.
Choosing for the Season
Both groups have cool-season and warm-season choices.
Cool-season cover crops
These are sown in late summer or fall and grow through the cooler months.
- Legumes: Austrian winter peas, hairy vetch, crimson clover, and red clover.
- Non-legumes: barley, oats, cereal rye, winter wheat, and brassicas.
Clemson Extension notes that oats may die during cold winters.
Cereal rye grows quickly in spring and can be sown later into the fall.
Warm-season cover crops
These fill a bed during summer, often between spring and fall vegetables.
- Legumes: cowpeas and soybeans.
- Non-legumes: buckwheat and sorghum-sudangrass.
Buckwheat is a favorite quick cover.
It sprouts fast, shades out weeds, and its flowers attract pollinators.
Cowpeas tolerate heat and drought well.
Planting dates vary by region.
The Clemson dates are for South Carolina, so ask your county Extension office about local timing.
How Much Seed to Use
Cover crop seed is usually measured in pounds per 1,000 square feet.
A raised bed four feet by eight feet is 32 square feet.
That is only about three percent of 1,000 square feet.
So a small bed needs just a handful or two of most seeds.
Clemson Extension lists these example rates for 1,000 square feet:
- Crimson clover: about one half to two thirds of a pound.
- Cereal rye: about two to four pounds.
- Oats: about two and a half to four pounds.
- Buckwheat: about one and a half to two and a half pounds.
- Cowpeas: about one to two pounds.
Follow the rate on your seed packet when one is given.
Step 1: Clear and Prepare the Bed
Remove weeds and any leftover plants from the last crop.
Loosen the surface and rake it level.
A smooth, loose surface helps seeds touch the soil evenly.
Step 2: Sow the Seed by Hand
For a home garden, hand sowing works well.
Clemson Extension suggests broadcasting the seed as evenly as possible.
Walk back and forth over the bed several times, scattering a little each pass.
This spreads the seed more evenly than one heavy pass.
Then rake lightly to press the seed into contact with the soil.
Water if the weather is dry, so the seeds can sprout.
Step 3: Let It Grow
Now the cover crop does the quiet work.
Its roots hold the soil and open small channels for air and water.
Its leaves shade the ground and crowd out weeds.
You do not need to fertilize most cover crops.
Clovers do best when soil pH is between 6.0 and 7.0.
Our guide to taking a soil sample shows how to check your pH.
Step 4: Cut It Down at Flowering
Timing matters here.
Clemson Extension recommends ending the cover crop while it is flowering.
At that stage it returns the most biomass and nutrients to the soil.
Do not wait until it sets seed.
Seeds left behind can turn into weeds in your next crop.
In a small garden, you can cut the plants with a mower, a string trimmer, or hand shears.
Step 5: Choose No-Till or Tilling
After cutting, you have two options.
Leave it on top
The cut plants can stay on the surface as a natural mulch.
This is called no-till.
You plant your vegetables through the layer of residue.
It works like the mulch in our guide to mulching garden beds.
Turn it into the soil
You can also chop the plants and mix them into the top layer of soil.
Clemson Extension advises doing this about three weeks to a month before planting.
That gives the plant material time to break down first.
Why Patience Pays
Soil life turns the cover crop into organic matter over time.
Clemson Extension explains that using cover crops for several years slowly raises organic matter.
Earthworms and helpful fungi become more active.
The soil grows looser and easier for roots to explore.
Organic matter keeps breaking down, so soil building never really ends.
Each season of cover crops adds a little more.
Cover crops also work well alongside a backyard compost pile.
A Simple Cover Crop Checklist
- Pick a cover crop that fits the season.
- Try a legume and grain mix when you can.
- Inoculate legume seed at planting.
- Clear, loosen, and rake the bed level.
- Broadcast seed in several light passes, then rake it in.
- Cut the crop down while it flowers, before seed forms.
- Leave it as mulch, or turn it in three to four weeks before planting.
A Calm Way to Begin
Start with one empty bed this fall.
A simple mix of clover and rye is easy to sow and pretty to watch.
By spring, you will have green cover where bare soil used to be.
Your next vegetables will grow in soil that is a little richer than before.
Sources and Further Reading
- Clemson Cooperative Extension, Home and Garden Information Center — Cover Crops: supports the benefits, legumes and inoculants, non-legumes, mixes, cool- and warm-season choices, seeding rates, sowing, ending at flowering, no-till and tilling timing, and long-term soil building.
- Sustainable Agriculture Research and Education — Managing Cover Crops Profitably: an in-depth handbook on cover crop species, rotations, and management for readers who want more detail.