Cover Crops in Community Gardens

Prepared by guest contributor Samuel Garrett McKee with assistance from David Neely and Margaret Rossano. Garrett is a garden leader of the Circus-Lyons Community Garden.

Cover crops have become increasingly popular in the past several years, seeing use from large-scale producers down to mid- and small-scale operations. Originating in pre-industrial times, cover crops have been an organic and sustainable, tried-and-true, method of using naturally occurring cycles to benefit soils for hundreds of years. The benefits are clearly seen once implemented, even at the community garden plot scale (10×10 ft, for example). At the Circus-Lyons Community Garden, we have been using cover crops for the past two years with solid results.   

Essentially, when a garden plot would otherwise be unused, we “cover” that soil with a special crop of plants, the purpose of which is to feed the soil, rather than to feed the gardeners. Several weeks before you want to use that plot again for annual planting, the crop is cut down and the plant matter incorporated back into the soil. Fall is a great time to start implementing a cover crop at your garden. Read on for more information and detailed advice.

cover crop planted in October that survived the winter and is growing well in February
Feb. 3, 2019. Cover crop planted in late October, cereal rye, Austrian winter peas and crimson clover. Established before coldest weather hit, overwintering well even with a real winter.  It’s merely waiting for longer warmer days and will likely be a foot tall by April 1.

The amount of information on cover crops can be daunting when you first begin the research, however, clarity can be found by thinking of cover-cropping as reminiscent of natural cycles. Central Missouri was once home to native tall-grass prairie ecosystems: perennial grasslands that harvest sunlight during the growing season and put the resulting carbon into plant  tissue, which is in turn harvested by grazing animals or consumed by wildfire, thus promoting plant competition and further unimpeded growth and diversification. This cycle was carried on without human intervention, adding yearly inputs to the soil.  

Typically, gardeners and farmers plant annual crops during a growing season, fertilize with off-site inputs, harvest, remove any residue of the crop, and then consider things finished. This leaves our soil more or less bare during the winter season, opening up invasion opportunities for weeds as well as the potential for erosion. This system is not reliably found in the natural world where there is continuous biological activity in the soil, year-round. This is what cover crops aim to fulfill.   

rye and clover cover crop with soil probe showing deep rich soil
Jan. 28, 2017. Cereal rye and crimson clover cover crop with soil probe showing the color you’re looking for!

Effective cover-cropping imitates a prairie system in that it provides more overall diversity and duration of biological activity to a plot. It can also stabilize soil; armor against weedy species and erosion; improve water capture/infiltration into subsoil; and improve the soil’s physical, chemical and biological makeup. Many resources exist for guidance on the matter, however, I will speak for what has worked for us at the plot level in our community garden.


Species Selection

Species used are many and again can be daunting to the beginner.  I tend to think about them in botanical terms; grasses (graminaceae), forbs (many families, but you can think of them mainly as flowers), legumes (fabaceae). 

Grasses

Species include cereal rye, oats, annual ryegrass, winter wheat and sorghum.

Pros: Grasses are competitive against weeds (including Bermuda grass!), they establish quickly and reliably, and they can be harvested for grain, mulch or hay, or even grazed. Grasses scavenge soil nutrients that would otherwise leach out or be taken up by weeds. Also, they are usually very winter hardy, easy to plant in fall and inexpensive. Species include cereal rye, oats, annual ryegrass, winter wheat and sorghum.

Cons: Grasses can easily out-compete forbs or legumes planted alongside them, detracting from overall benefits of diverse cover crop plantings. Cereal rye, upon termination, suppresses weeds and/or seed germination allelopathically in the soil, meaning that compounds released by the rye as it is killed will stifle germination of other species for a short period.  A solution to this minor issue would be to allow two to three weeks of inactivity between termination and the next planting.

cover crop planting at community garden
April 23, 2018. Cereal rye, crimson clover, winter wheat adjacent to hand tilled, just terminated cover crop

Forbs

Species include radishes, turnips, buckwheat, and sunflowers.

Pros: Forbs usually have deeper root systems that scavenge/capture nutrients in the topsoil that are unavailable to many crops. The, provide bloom and beauty, and some can be harvested for seeds or flowers, or they can be grazed.

Cons: They are sometimes slower growing or difficult to get established, and they sometimes cost more.

Legumes

Species include clovers, vetches, winter peas, black-eyed peas (cowpeas).

Pros: Legumes sequester nitrogen from the atmosphere and make it available to plants in the rhizosphere (rooting zone). They provide beauty and blooms for pollinators, and can be grazed or harvested for hay/mulch.

Cons: They are they usually slower to establish than grass, and the seed should be inoculated prior to planting. Red clover is a perennial and will persist when not desired, and vetches are semi-aggressive invaders into both urban and wild environments.


Fall Cover Crops

After the summer garden crops have played out and freezing temperatures are on the horizon, you should be thinking of cover cropping by October through mid-November.  The trick is to get the crop established and at least 4- to 6-inches tall before the harsh temperatures set in. Species that work well at this time include Austrian winter peas, crimson clover, cereal rye, winter wheat, and oats. Doing a two to four species mixture seems to work well, as each year is different and having multiple species to fill in unexpected gaps is ideal. Cereal rye, crimson clover and winter peas have been a good combo for us at Circus-Lyon garden. 

Late Winter/Early Spring Cover Crops

Similar species as work in the fall will also work from late February through March and even into early April. Snap peas could be viable for this outcome, as well, since they are a legume. We’ve even had seed sown in January warm spells that germinates in early March and grows vigorously all throughout spring. 

Summer Cover Crops

After a spring crop is harvested, you can plan to seed a cover crop into an otherwise fallow plot.  Species which work well for this would be buckwheat, mustard greens, annual sorghum, black eyed peas or anything which can handle heat, sunshine and long growing days. Buckwheat puts out a long taproot, bringing otherwise unavailable nutrients up into your plot’s topsoil as well as providing much-needed blooms for pollinators. However, if left to go to seed, buckwheat will seed your plot in many little individuals that will compete with desired crops when given the opportunity! Cowpeas (or Black-eyed peas) are a great legume choice for summer. 

buckwheat cover crop planted in summer amongst other garden vegetables
Aug. 5, 2017 Buckwheat establishment following sweet corn.

Terminating Your Cover Crop

Cover crops must be “terminated” once the time rolls around for planting of desired food crops.  Many ways exist to do this, but I will detail the way which has worked for us. First we mow or weed-eat the cover crop about two to three weeks prior to our desired planting date. We let the residue of the cover crop sit for several days after mowing, then turn it by hand into the soil using a shovel or a tiller.  Small plots are best done by hand. Be sure to break up the clods and root systems while turning it over, and try to get dead plant matter buried. This provides food for earthworms and countless other micro biota in the soil to consume and make available for your soon-to-follow food crops. Some warmer season cover crops, such as oats or buckwheat, will self-terminate, or winterkill, when exposed to cold temperatures. This is also a convenient time to incorporate compost into the soil to feed the incoming crop.  

cover crop mowed down and tilled in
March 30, 2018. Mowed cover crop adjacent to mowed, then tilled cover crop.

Optionally, legumes and forbs can be allowed to flower before you terminate them, which provides blooms for native pollinators and honey bees (crimson clover is worth growing for the flower alone!). Buckwheat seed can be harvested easily enough by hand and used the following year, or ground into gluten-free flower. Cowpeas and snap peas can be harvested for consumption.     

A good cover crop is a species that “behaves” in an agricultural setting, meaning it doesn’t escape or become invasive, is an annual, doesn’t persist after termination, and is consistent in establishing  and flowering like any other crop. A cover crop’s ability to suppress weeds is perhaps its most powerful feature, as the ideal period after termination to planting is a very short window, excluding many undesirable weed species otherwise abundant in our community gardens.


Summary

In summary, cover crops provide a suite of benefits to your garden plot including improving soil structure, fertility, water holding capacity and overall diversity; weed suppression; carbon sequestration; soil conservation; and supporting earthworms, pollinators and wildlife habitat. We have ordered cover crop seed through Wilson’s Garden Center or picked up larger custom amounts from Bourn Feed and Supply Inc., both located here in Columbia.   

Another wonderful benefit you will notice immediately is the aesthetic beauty the verdant, lush cover crops provide during otherwise dreary times of year. As the great conservationist Aldo Leopold once wrote,

“A thing is right when it tends to preserve the integrity, stability, and beauty of the biotic community. It is wrong when it tends otherwise.”

Cover crops can help community gardeners accomplish this simple yet powerful truth.