Just when my garden most resembles a dying jungle of dry cornstalks, defoliated tomato plants and yellowing leaves of all sorts, I realize it’s almost past the time for planting cover crops. So I must enter the jungle, dig up, cut back and put all the dying, dead and unwanted plants out of their late-season misery.
At the edge of my corn patch, for example, there’s a lone stinging nettle. It was such an intriguing and lovely thing, I let it grow. Its purple flowers amused me: They look like little pot scrubbers. But sometimes, as singer Nick Lowe said, you have to be cruel to be kind. The pretty nettle must go.
Before tackling the garden, however, I garnered some tips from Carl Evans during a recent workshop sponsored by the Reems Creek Nursery in Weaverville, titled “Soil Building With Cover Crops.”
“There’s a real science and art to building healthy soils with cover crops,” says Evans. With his wife, Julie Mansfield, he runs Mountain Harvest Organics in Madison County’s Spring Creek community. Cover crops can head off soil erosion, capture nutrients, suppress weeds, improve soil structure, add organic matter, promote drought tolerance and more.
Consider this: A typical 50-pound bag of 10-10-10 fertilizer contains a mere 5 pounds of nitrogen. For small-scale gardeners, a half-pound of crimson clover planted on a 1,000-square-foot plot produces 5 to 10 pounds of nitrogen. That’s the equivalent of a $20 bag of fertilizer. Clover seed—and an inoculant that helps maximize its nitrogen production—will probably cost less than half that, he calculated. Planting cover crops instead of buying, hauling and spreading fertilizer is very cost-effective, Evans maintains.
“Start small, if you haven’t done [cover crops] before,” he counsels. Now’s a good time to plant fall cover crops—clovers, rye, oats, hairy vetch, Austrian winter peas, buckwheat and such, he noted. Each crop provides particular benefits: Legumes—the clovers, vetches and peas—fix nitrogen in the soil, which will help next summer’s corn crop. Buckwheat grows rapidly, suppresses weeds and makes soil-bound phosphorus more available for the next crop. Spring oats will be killed by heavy frost, leaving a natural mulch that combats erosion. Cover crops with deep taproots, such as white clover, break up heavy soils. Dwarf white clover has the added benefit of withstanding foot traffic when planted in garden walkways.
To maximize such benefits, Evans likes a bi-culture: combining a cereal grain with a clover, for instance. A heavy frost kills the grain; the clover remains dormant through the winter and resumes its growth come spring. A rye/clover combination works well as a precursor to your late-spring and early-summer crops. Austrian winter peas and spring oats benefit your early-spring crops, Evans explains.
The downside to the latter combination is that deer love the peas and will “graze it to the ground,” he notes. Evans solved that problem by setting an 8-foot-high, $10,000 fence around his 5-acre growing area.
Whatever cover crops you choose (and however you choose to deal with deer), the general idea behind these “green manures” is simple: At some point in the growth cycle, “You kill it and incorporate it,” says Evans. Often, a heavy frost will do the job; otherwise, you may need to cut ‘em down yourself. It’s the timing that’s tricky. When about a quarter of the clover is blooming, mow it or till it under for the highest nitrogen benefits. Let your cover crops get too high—especially the grains—and they’ll re-seed, becoming pesky weeds. Evans admits that he often lets his rye get too tall, but if you’re a small-scale or home gardener without access to heavy-duty equipment, you need to cut, kill or turn your cover crops under without delay. Here in the mountains, the timing of all these activities can vary a great deal; at some higher elevations, it may already be too late to plant some cover crops before our first hard frost comes along, says Evans.
Some cover-crop choices are personal, he notes. “My neighbor calls hairy vetch ‘tangle weed.’ Its vines will wrap around your tiller, and you’ll be cussing me and the vetch,” he says. For that reason, Evans stays away from it.
My local farm-supply source is an older native Tennessean who’s usually chewing tobacco when he answers my questions. “Vetch and clover—those go together around here,” he insists.
Evans, however, laughs at my tale and emphasizes the variety of combinations to try. Mustard and rape make a good mix, he muses. “You know how hot the mustard seeds are to eat? [As a cover crop], they give off fumigants that kill [the bad] nematodes.”
Experiment and see what works, he suggests. Try growing fescue between blueberry plants (but keep it mowed and several feet from the bushes, so it doesn’t suck nutrients or moisture from your blueberry crop). And next season, sprinkle cover-crop seeds between established vegetables. This “undersowing” is of particular benefit when growing corn organically, says Evans.
It’s good to keep an innovative spirit, too. In his greenhouse, Evans spread rye straw and broadcast clover directly into it, without prepping and raking the soil as he usually would. “The tiller was broken and I had no other way,” he confesses. “But I got great results.”
There’s also a labor-saving element, he concludes. “Cover crops are a good way to go. If you can plant something, mow it and let it grow … why go to all the trouble of having to spread all that compost?”
[Evans can be reached at firstname.lastname@example.org. Garden editor Margaret Williams can be reached at email@example.com.]