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Turning Cover Crops into Green Manure

Cover crops planted in the fall are now growing like weeds. But now what do you do with them? They should be turned into Green Manure! Time to knock down your cover crop. In our video on Green Manure, Tricia talks about when and how to turn your cover crop into a fantastic soil additive.

Timing of the Knock Down

The timing is determined by when the next crop will be planted and the life stage of your cover crop.

  • Cut down your cover crops before they go to seed.
  • A good indicator for when to knock down the cover crop is when one half of the crop is flowering. This allows you to take advantage of maximum biomass.
  • After cutting, let it decompose so that you get the maximum benefit to the crop that you're going to plant afterward.
  • After cutting, allow at least 3 to 6 weeks before planting your next crop. It's important to wait because your cover crop will be decomposing and during this decomposition process you will temporarily lock up some of the nitrogen in the soil.

Speeding up Decomposition

You can speed up the breakdown process of your green manure by adding something like our Biodynamic Field Spray. The spray adds beneficial bacteria that speeds up the break down of the green manure to about two weeks. When using this product, make sure you use dechlorinated water when mixing. After application of the spray, turn under the plant matter.

What is the Best Way to Knock Down the Cover Crop?

There really is no best way. It depends on the tools you have on hand and the amount of cover crop you want to turn into green manure. You can cut it and compost it, you can weed-eat it or mow it and just let it lay on the ground, or you can till it into the ground.

The three main methods of cutting down cover crops are: undercutting, mowing and rolling. Undercutting is when you draw a blade under the soil and you slice the cover crop underneath the soil. For mowing you're going to mow down the crop with your lawn mower a weed whacker, or a scythe. This chops the crop up fairly finely and it will decompose quickly. Rolling is basically running your tiller over the plants with the tines turned off. However, this may not always kill the plant and thus not decompose.

Tilling or Rolling

  • Tilling it in is the fastest and easiest way to incorporate your cover crops.
  • Rototill the crops into the ground.
  • The advantages of this method are faster decomposition and less nitrogen loss into the atmosphere.
  • The disadvantage is that you don't get the weed suppression or water conservation while the crop decomposes.

Cut it and Compost it

  • You can use a hand sickle, a scythe, weed-eater or mower.
  • The advantages are that you're adding finished nutrient-rich compost back into the soil (eventually).
  • This is a great option for raised bed cover cropping.
  • The disadvantage is that it's more work to cut, compost and then add the compost back into the soil and it can take several months instead of weeks.

Mow or Weed-Eat

  • After cutting the cover crop down, let it lay on the soil surface as a mulch as it decomposes.
  • This will help with water conservation and weed suppression.
  • This method chops the cover crop into small pieces and will speed up decomposition.

No matter what method you choose, the most important thing is that you will be improving your soil with the addition of green manure!

22 comments

  • Debbie, you can keep your cover crops trimmed and let the trimmings lay in your bed. The cover crop will eventually die due to high temperatures. You should not let them go to seed since this pulls the nitrogen from their roots into making seed. This kind of defeats the purpose of adding a nitrogen producing cover crop.

    Suzanne at GrowOrganic.com
  • I have a cover crop growing right now in my raised beds, it’s beautiful actually, my hope was that I can trim and let fall and leave the plants there to keep growing and keep trimming, so I didn’t want to compost separately and I didn’t want to roll in yet with the tiller.

    Is this ok? is it better than if I wasn’t doing anything, or am I wasting my time with no benefit this way?

    Thanks, going more and more organic every day!!!

    Debbie
  • Katie, cutting and turning should be enough to to kill the cover crop. You can also, when you are turning it, leave the root ball exposed to the air so it will dry out. Another thing you can do is cover it with some black or dark green mulching fabric. This will heat up the soil and also keep any sun from the plant.

    Suzanne at GrowOrganic.com
  • I planted a cover crop mix in my raised beds last fall and turned the cover crops under about a month ago (but did not mow or weed-eat them first). They re-established themselves and now are huge! Will just mowing them and then turning under kill the roots/keep them from continuing to grow back?

    Katie
  • Farmer Bob Cannard recommends allowing the cover crop to go through its entire life cycle before cutting it down.

    Molly Collum
  • Laurie, you can cut them any time, but keep in mind that the longer you let them grow the more biomass you will have and more time the legumes will have to fix nitrogen. So cutting before they start to flower is ok. Sounds like you are on the right track. Not sure what kind of cover crop you planted, but we do have a cold zone mix that is good for higher altitudes, Peaceful Valley Cold Zone Soil Builder Mix – Raw Seed. You may also want to consider covering with a floating row cover if you are anticipating below freezing temperatures.

    Suzanne at GrowOrganic.com
  • I planted my cover crops in the fall in my raised beds, which are 28" tall. The covers did not have time to sprout prior to winter. It is now the first of April and the seeds have just begun to sprout. The soil is 50 degrees. I removed the winter mulch (hay) so the covers will be able to see the sun and grow. It will still freeze & snow before I can plant here at 9,000 feet, and my “last frost” is around June 9-15. I’m hoping to get enough growth out of them to turn them under by mid-to-late May. I’m wondering if it might be best to cut the tops off the covers at that time, put those tops into a compost pile, then turn under what remains of the stems and the roots. I suppose I should consider the “Biodynamic Field Spray” to speed up decomposition. Am I on the right track? I’ve never planted cover crops before. (I was pleased to see that they are already sprouting!)

    Laurie
  • Molly, Everything I have read, advises to cut down your cover crop after it is about have in flower. This way the plants are at their max biomass production. In addition, you don’t want your plants to make seed to be dropped in your field or garden plot.

    Suzanne at GrowOrganic.com
  • Ben, You might be better off planting the Cold Zone Soil Builder Mix. https://www.groworganic.com/cold-zone-soil-builder-mix-raw-lb.html
    It really depends on when you can plant it. If you plant it in the fall, you should do so soon, so it has enough time to establish itself and grow before winter sets in. It will get knocked back by the cold but should regrow come spring. Or you can plant it in the spring (probably late spring) as soon as the soil is warm enough. If you plant it in the fall, don’t cut it down until the late spring/early summer before you are ready to plant your garden.

    Suzanne at GrowOrganic.com
  • Im a little confused, this is my first time with cover crops. I have 3 80sq ft. raised beds. I have only hand tools and a weedwacker. What happens if I plant the premium soil builder in august or september in Ohio? Do i chop it down come winter and will it regrow in spring?

    ben

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