Winter Cover Crop Chart

Most vegetables set fruit at maximum temperatures of 90°F or less, so this summer’s sweltering temperatures in much of the U.S. have been a challenge. High tunnel production has been especially difficult, as temperatures can routinely go over 100°F on a sunny day.

Oats are a low-cost, easy-to-use cover crop, provided the temperatures are right. They are a cool-season annual cereal (grain) crop. We like oats as an over-winter cover crop because they reliably winterkill in our zone 7a climate (average annual minimum temperature range 0-5°F (-18C to -15C). In warmer zones, even 7b, the temperatures do not always get cold enough to kill them. Large oat plants will get serious cold damage at any temperature lower than about 20°F (-7C) and will die completely at 6°F (-17C) or even milder than that. (Sources differ in their opinions about the winter-kill temperature for oats. 20°F seems a safe bet.) If they die, they are easy to till in, and if they don’t die, they are still easier than rye. The best resource on cover crops that I know is the SARE book Managing Cover Crops Profitably. You can buy the book or download the free pdf from their website http://www.sare.org/Learning-Center/Books. Another benefit of using cover crops is that they help sequester soil organic carbon, see http://news.aces.illinois.edu/news/cover-crops-can-sequester-soil-organic-carbon.

Disease pressure from late blight was high during the summers of 2012 and 2013, and I made a fair number of farm visits looking for the pathogen. Once the disease was found in New Jersey and the weather conditions were conducive to its spread the alert went out to growers that they should use preventative sprays.  Organic growers rely on copper-based fungicides as a protectant for many diseases, and in the case of late blight this is the only current organic option shown to have worthwhile efficacy.  During the summer I repeatedly witnessed a philosophical struggle with the idea of using copper.  Which was the lesser of two evils – copper or late blight?  Tomatoes are an expected crop at a diversified vegetable farm and a staple for producers here in NJ.  “But what is it doing to the biology of the soil” was the theme from growers. A literature search showed some research, but not a lot of data on soils from active farms with a history of using copper. 

In the last issue of GFM, I wrote about using clovers as cover crops. If you are looking for a legume that can be sownseveral weeks later in the fall than clovers, Austrian winter peas could fit the bill. Like clovers, they will discourage weeds, add nitrogen and biomass to the soil and prevent erosion. When flowering, Austrian winter peas also attract beneficial insects (especially honeybees) and reduce aphids.

There are many types of clover used to discourage weeds, add nitrogen and biomass to the soil, and prevent erosion. In addition, clovers attract beneficial insects and reduce aphids. The main uses for clovers are: as overwinter cover crops; green fallow (full-year cover crops); undersown in existing food crops; and no-till or reduced-till crop sowings in standing clover. I’ll talk about each of the uses we have tried, and look at the various types of clover and their requirements.

Buckwheat is a fast-growing warm-season broadleaf annual that is a useful cover crop. Its special strengths are in suppressing weeds, attracting beneficial insects, improving the soil tilth 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 10 times better than rye.

Cover crops are a big part of my fertility program. I use them in an attempt to keep nutrients cycling in the soil, to improve soil texture and organic matter, to add nitrogen, to displace weeds and to provide habitat for beneficials. Because cover crops aren’t directly generating income like a cash crop, it’s hard for me to give them as much attention as they deserve. That said, they can be quickly and easily seeded using some pretty basic tools and a bit of planning.

Radishes should not be overlooked – although usually a minor crop, they have some important roles in a mixed vegetable farm. The familiar small radishes are quick-growing, brightly colored and add crunch to winter and spring salads. Since they are easy and quick to grow, they can be planted whenever a space opens up, as insurance for filling out the CSA box or market booth. And if you don’t need them, you haven’t invested much, and can till them in. Or let them flower, as the flowers attract beneficial insects. Not all round and red, radishes come in many shapes and sizes to add visual variety. There are also large winter storage varieties, and ones for use as a cover crop, which can help control pest nematodes.

Selecting a good tool and keeping it in working order is only one piece of any job.  While it is a critical piece, it cannot be separated from the need to understand how the tool works. There are a lot of aspects to the way a tool works: timing, the physical manipulation of the tool, and also recognizing the limitations and even drawbacks of the tool, recognizing when not to use it.

Southern peas have many names. There are three basic types: mild-flavored Blackeye Peas (Queen Anne, Pink Eye Purple Hull, Bettergro bush, Princess Anne, all bush or semi-vine types), stronger-flavored Crowder or Conch Peas (Colossus, Hercules, Mississippi Silver, Mississippi Purple, Zipper Cream, Dixie Lee,), and the mildest-flavored Cream Peas (Bettersnap, Lady, Tender Cream, Texas Cream are all bush types).