Turning Cover Crops into Green Manure

Cover crop green manure

Using Cover Crops to Improve Soil Health

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.

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!

Find more information on no till in your garden in our resource center.

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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!!!


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?


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

Molly Collum

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