Cover Crops for March: Sowing Options and Incorporating Cover Crops

In March, where we undersowed clovers in the broccoli patch in August, the old broccoli trunks are surrounded by a sea of green clover.
Photo by Kathryn Simmons

In December I wrote about Cover Crop Planning for Next Year, including 5 steps of cover crop planning for all opportunities. I have a slideshow Crop Rotations for Vegetables and Cover Crops, which I find to my surprise that I haven’t posted here since my 2014 version.

Here it is now

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In January I shared some resources to give the Big Picture of Cover Crops, including a compilation of slides for SARE (Sustainable Agriculture Research and Education) and my slideshow Cover Crops for Vegetable Growers.

In February, I described limiting winter annual weeds by sowing oats in spaces without a cover crop and no planned food crop for 6-10 weeks. Six–ten weeks (depending on your climate) is long enough in early spring to get worthwhile growth from oats before prepping for the food crop.

This month I will include some options for cover crops you might sow in March (in central Virginia and similar climates), and then talk about incorporating cover crops, which surely you will be doing this month!

Cover crops to sow in March, and other options

Purple stemmed mizuna. Mizuna and other frilly mustards are fast-growing crops, attractive to the eye and the palate.
Photo Pam Dawling

Depending on the stage of the year where you are, you could revisit any of those posts.

  • In early March the oats plan still works for us.
  • In early spring, the air and the soil are cold, and sowing a fast-growing vegetable crop will not be successful with a gap of less than eight weeks. Crops take too long to grow at this time of year.
  • If you have more than eight weeks you could try those fast-growing vegetables: kale, spinach, Tokyo bekana, radishes, chard, lots of salad crops, senposai, mizuna, tatsoi, land cress. Or try Eat-All Greens, an idea from Carol Deppe. Patches of carefully chosen cooking greens are sown in a small patch. When it reaches 12″ (30 cm) tall, Carol cuts the top 9″ (23 cm) off for cooking, leaving the tough-stemmed lower part, perhaps for a second cut, or to return to the soil.
  • In late March or April in climates like ours, we can sow winter wheat or winter rye – they will not head up, but will “wimp out” when it gets hot. That is, they will stop growing, so you won’t get a lot of biomass, but you will have some live roots in the soil, holding it together and taking care of the soil microfauna, and discouraging weeds form germinating. One year when our spring-planted potatoes got flooded, we transplanted potato plants to the drier end of the patch and sowed winter rye in the lower end, once the floods had subsided. This kept the soil covered, scavenged the compost we had spread for the potatoes, and was easy to deal with in July when we harvested the potatoes. It was also much more hopeful; to look at an area of green cover crop than an area of green weeds!
  • Once we get to March 31 here, it is too late in the year for us to sow oats (they will quickly head up after making very little growth) and too soon to rely on frost-tender cover crops. See the section in February’s post on the Stale Seedbed and Tarping Techniques.

    Tarping beds to kill weeds.
    Photo Cornell Small Farms Unit
  • By mid-April, it is an option to sow a mix of oats and buckwheat. The oats will protect the buckwheat somewhat from the cold. I’ll come back to that idea next month.

Incorporating cover crops, or not

See Barbara Pleasant: How to Take Cover Crops Down. Gardeners working with small tools can start by mowing their live cover crops, grazing poultry on them, or scything them and hauling them aside to use later for mulch. On a very small scale, you can pull your cover crop plants, although I think it is valuable to leave the roots in the soil. On a larger scale, you can graze larger animals, or cut the cover crop down. If the cover crop was winter-killed, the stems will easily disintegrate, so you can skip the cutting down part of these instructions.

If you plan to incorporate the cover crop, choose a mowing method that cuts the plants into small pieces, making them easier and faster to incorporate. On a small scale, this could be a weed whip or a lawn mower; on a larger scale a bush hog. If you plan to use the cover crop for mulch, cut it in a way that leaves the stems as whole as possible. On a small scale this means a sickle or scythe, on a bigger scale, the kind of machinery you might use to cut hay.

Cover crop of rye, vetch and crimson clover in March.
Photo Kathryn Simmons
Rows of Roma paste tomatoes, some on bioplastic, some no-till. Credit Bridget Aleshire

After getting the cover crop down, you could tarp for a minimum of three weeks (allow for more), or you could work the residue into the soil, with a chopping hoe or by digging it in, or using a walk-behind two-wheel tractor such as BCS with a rototiller or a power harrow, or a four-wheel tractor and discs. Cornell has posted a webinar Pairing Tarping with Cover Crops, by Brian Marr.

If you incorporate the cover crop into the soil green, you will also need to wait two or three weeks (or more in early spring) to plant or sow, to give the cover crop time to break down in the soil before it can be available for your crop.

Winter rye produces allelopathic substances that can temporarily inhibit the germination and growth of small seeds. Wait three weeks after turning under before sowing. Transplants don’t suffer the same problem. Oats, wheat, and other cereals also have this tendency, but to a much smaller degree, usually small enough to ignore. Sorghum-Sudan grass hybrid incorporated fresh in the soil hinders the growth of tomatoes, lettuce, and broccoli, but that’s a summer cover crop you won’t need to think about for several months.

I still haven’t got to my Conference notes on cover crop workshops, 2023-2024, but this is enough for one post!