Cover Crops for December: Planning for Next Year

Our asparagus patch mulched for the winter.
Photo Kathryn Simmons

 

Keeping the Soil Covered all Winter

Don’t plant cover crops in December, unless you live in a warmer place then Zone 7a. Weeds will be our cover crop for the next few months! You can mow the weeds anytime you see lots of flowers and seed heads. For us, it’s usually one mowing in November, then no more until early February.

If you are later than 3-4 weeks past your average first frost date, leave the weeds or crop remains growing. It’s too late to sow a cover crop, and you’ll do more harm than good tilling up the soil.

Having plants growing through the winter, or at least into the winter until they get killed by cold temperatures, will improve your soil both physically (the roots hold the soil in place, preventing erosion, and they open up channels that improve the drainage) and biologically (the soil micro-organisms thrive when they have active plants to cooperate with, exchanging nutrients).

If you are less than 3 weeks past your first frost, see my post Cover Crops for November. It is still worthwhile to sow a few cover crops up to three weeks past your average first frost. If the area is ready for cover crops up to 10 days past the frost date, sow winter wheat or winter rye and hairy vetch or Austrian winter peas. Two or three weeks past your first frost, you could sow winter rye. Winter rye is hardier than any other cover crop and can take later planting dates. If you don’t have winter rye, don’t till! Leave the weeds.

You could mow and tarp, to kill the weeds before spring. I’m not sure what the soil life thinks about that, though!

If you don’t have weeds, but only almost bare soil, and it’s too late to sow cover crops, find some kind of organic mulch. Cardboard weighted down with bricks or rocks is much better than nothing.

Be prepared to act early in spring, so you don’t get weed seeds. You could mow in early spring, or till and sow oats, if you won’t be planting a food crop in the following 8 weeks, giving the oats time to make respectable growth before turning them under.

This rye cover crop is still small in early March, but will soon make rapid growth.
Photo Pam Dawling

Plan Cover Crops for Next Year

Our other cover crop related task is planning for next year, and ordering seeds. See Planning Winter Cover Crops, a post that includes my Short Simple Guide to Winter Cover Crops.

Choosing the “perfect” cover crops can be confusing, but any is better than none, so I encourage you to experiment and keep records, so you can improve your choices each year. It helps to know your average first frost date, and your winter-hardiness zone (the lowest temperature your garden is likely to encounter).

Create a crop rotation for vegetables that includes good cover crops

If you haven’t yet made a plan for next year’s cover crops, a good time to do it is when planning the crop rotation for your vegetables. You can tweak your plan to maximize your cover crop opportunities.

Here’s 5 steps of cover crop planning:

  1. Identify your opportunities for cover crops (When, how long, how warm, crops before and after)
  2. Clarify your cover crop goals for each opportunity (check list of benefits above)
  3. Shortlist suitable cover crops for each situation (consult books and charts)
  4. Make a decision from among the options to match your main goals and some secondary goals
  5. Record your decisions and results, and review for possible changes next year.
Sunn hemp cover crop at Nourishing Acres, North Carolina.
Photo Pam Dawling
Step 1 – Cover crop opportunities
  • In fall after food crops, for the whole winter – the easiest place to start
  • In late winter or early spring, if the area will not be planted with a food crop for 6 weeks or more.
  • In spring, summer or fall, whenever you have 4 weeks or more between one vegetable crop and a later one
  • Undersowing at last cultivation (usually 4 weeks after planting the vegetable crop)
  • To replace a crop failure, smother weeds, make use of the compost you provided for the failed crop.
  • Year-round cover crops (green fallow) if you have a space you will not be using for vegetables in the coming year.
Step 2 – For each opportunity, clarify your cover crop goals

Which cover crop benefits are your main priorities and your secondary goals at that site?

  • Smother weeds, prevent them growing and seeding
  • Add organic matter and nutrients
  • Increase the biological activity in the soil
  • Reduce erosion by using actively growing roots to anchor the soil
  • Improve the tilth of the soil and the sub-soil structure
  • Improve soil drainage
  • Improve the soil’s ability to absorb, hold water
  • Salvage leftover nutrients
  • Fix nitrogen to feed the next crop
  • Attract beneficial insects
  • Bio-fumigation for pest or weed control
Step 3 – Choose cover crops matching your goals
  • Smother weeds: sorghum-sudangrass, pearl millet, winter rye, wheat, barley, oats, buckwheat, brassicas, lupins, red clover, subterranean clover, berseem clover, soybeans, southern peas
  • Add organic matter, improve the soil’s ability to absorb, hold water: bulky grasses and legumes, sorghum-sudangrass, millets, winter rye, velvetbean, southern peas, sweetclover, sunn hemp (Crotalaria)
  • Increase the biological activity in the soil – use varied mixes
  • Reduce erosion: (good roots) grasses especially rye, barley, oats; also sweetclover, southern peas, sub clover,
  • Improve the tilth of the soil, the sub-soil structure, soil drainage: sorghum-sudangrass, sunflower, daikon, sweetclover, crimson clover, alfalfa, lupins, southern peas, forage radish, sugar-beet or forage-beet
  • Scavenge leftover nutrients: (non-leguminous cover crops) grasses, brassicas (pest and rotation problems), annual ryegrass (danger of it becoming a weed)
  • Fix nitrogen: (legumes) clovers, vetches, peas, southern peas, soybeans, lentils, sunn hemp.
  • Attract beneficial insects: (flowers) buckwheat, peas, beans, clovers, brassicas, phacelia, sunn hemp
  • Pest control: rye, brassicas, sorghum-sudan, sunn hemp, white lupins, sesame.
  • Kill nematodes: Pacific Gold mustard, white lupins, Iron and Clay southern peas, OP French marigolds, sesame
Iron and Clay southern peas flowering in September. Photo Pam Dawling
Step 4 – Choose cover crops for the fall and for the summer

Work back from your farm’s first frost date, to see what options you have in the fall. In the summer work with the length of time that plot has before you need it for another food crop.

Here’s my 7 steps of crop planning:

  1. Figure out how much area is needed for each major crop (the ones needing the largest amount of space).
  2. Measure and map the land available
  3. Divide into equal plots big enough for any one of your major crops
  4. Group compatible crops together to fill out each plot not yet housing a major crop
  5. Set a good sequence, maximizing cover crop opportunities
  6. Include best possible cover crops at every opportunity
  7. Try it for one year, then make improvements

For more details, see my slideshow Crop Rotations for Vegetables and Cover Crops on SlideShare.net

5 thoughts on “Cover Crops for December: Planning for Next Year”

  1. Hi, is it ok to broadcast cover crop seeds like rye if you are more than three weeks past your first frost date? It seems good to avoid tillage when the soil is so cold and wet and easily compacted, but if you could sow without compacting the soil, would there be any point in it? Would the rye make enough growth to make a difference?

    Also how do you feel about leaves as a mulch on bare soil? I have access to huge amounts of leaves, but I wonder if it will just create a slug epidemic if I put a lot of them down and leave them over winter.

    1. I agree with avoiding tillage this late in the year (in zone 7a). You could try broadcasting rye if you have some on hand. I don’t know if it will germinate. It will partly depend on water. Rye is a bit big of a seed to germinate just lying on the surface.
      I doubt the rye would grow much now.
      Also you might get lots of mice, squirrels, voles and worse eating the free seed!
      I wasn’t thinking about slugs when I suggested spreading leaves on the soil. Slugs do like all kinds of damp mulch. But they are not much in evidence here any longer, now it is getting colder.
      if I were choosing between leaving soil bare, or mulching and risking slugs, I’d mulch and keep an eye on nearby plants.
      Hope that helps.

      1. Later I was thinking that you could rake off the leaf mulch in early spring, before all the slugs start emerging and eating things. I wonder if that would work. I have not always had good results mulching with leaves in late summer: sometimes it actually seemed to kill brassicas if I put leaf mulch around them. It may be because there are sometimes walnut leaves in any mix of leaves that I rake up around here, whether on my own farm or elsewhere in the ‘hood. I think walnut leaves are not a problem once they are composted though.

        1. Thanks Shannon. that WSU link you sent was helpful, concise and clear. I see cabbage is listed as sensitive to juglone, so I’d guess other brassicas are also sensitive. Sounds like composting the walnut leaves would deal with the juglone problem. but that doesn’t answer your need for some way now, to cover your soil for the winter, other than leaving the weeds. And mowing them when they flower to prevent seeding.

          Anyone else out there got ideas? Has anyone had success with broadcasting a winter grain into weeds at this time of year?
          Pam

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