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September 23, 2019

The hoop house is not an easy place to grow cover crops. If you have designed yours so you can open up the ends and drive your riding tractor and implements through, you could grow cover crops. If you use a walk-behind tractor, you could grow the shorter, less rambunctious varieties. If you use only hand tools, this restricts any cover you consider.

Buckwheat, mustard, soy and cowpeas might still be options. The grass crops are hard to deal with using only hand tools. Using only hand tools reduces soil disturbance: Tillage burns up the organic matter. Secondly, you might not want to give up the space for cover crops when you could grow food crops in the wonderful protected environment. You might choose to bring in your nutrients from elsewhere, either from off the farm or produced at home.

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Some organic farmers in tropical areas replenish the soil by growing food crops for eight months and cover crops for four, even though winter conditions there don’t prevent growing food crops year-round. Hoop-house growers who do not need high summer crops could use that time to grow cover crops. Sweet potatoes or cowpeas are used as summer “smother crops,” (and you can harvest the sweet potatoes). Cowpeas (such as iron and clay) with a relatively upright growth habit compete better against weeds than prostrate types.

Many studies confirm the soil benefits of cover crops. The root channels improve the soil structure. Fine roots make up 70 percent of the root biomass of crimson clover, vetches and field peas. When the cover crops are mowed, these roots support microbial growth, form active organic matter and rapidly release nitrogen to the plants. So, if you can’t easily incorporate cover crops into your hoop-house soil, consider no-till types, which become mulch, or grow compost crops there. Cutting and removing the top growth to make a source of nutrients for later, or even for a field crop, still leaves the beneficial roots in your hoop-house soil.

year-round hoop house cover
New Society Publishers

Radishes as a cover crop can help control pest nematodes. I haven’t tried this, because harlequin bugs attack our brassicas and we don’t want to encourage more. Also, we need to keep crop rotations in mind, and we do grow a lot of brassica food crops. Mark Schonbeck includes them in his Cover Crops for All Seasons on the Virginia Association for Biological Farming website.

Use daikon, oilseed or fodder radish. Sow at 10 to 20 pounds per acre at a depth of 1⁄2 inch in early spring for maturation in June, in late summer to mature in October or to be winterkilled once temperatures reach 20 degrees Fahrenheit. Radish cover crops grow to a height of 1 1⁄2 to 3 feet and produce 1 1⁄2 to 3 tons per acre of biomass.

Radishes are semi-hardy crops that root deep into the subsoil, breaking up hardpan. They scavenge and conserve soluble soil nutrients, including nitrogen, and shade out weeds through their fast-growing canopy closure. Their strongly allelopathic root exudates inhibit weed seeds from germinating. They can also inhibit seeds of the next crop from germinating, but the effect subsides after a few weeks.

The SARE book Managing Cover Crops Profitably has good information on all kinds of brassicas as cover crops. Similar information is available from eXtension.org, under the Organic Agriculture Resource Area, including a webinar on winterkilled cover crops for suitable climates.

Pam Dawling. excerpted with permission from The Year-Round Hoophouse: Polytunnels for all seasons and all climates (2018) from New Society Publishers

This story originally appeared in the November/December 2018 issue of Hobby Farms magazine.

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