How to kill cover crop

danell(7)March 15, 2012

Okay, I'm new to this so please be kind.

I have dense heavy clay with little to no organic content and want to plant trees, shrubs, perennials. So for the past 1.5 years I've been adding things like compost, manure, coffee grounds. Last year I brought in 6 inches of compost and manure, planted a cover crop (rye, vetch, legumes, diakons) then when crop was 4 feet tall I chopped it down and tilled everything under. I then planted a second cover crop in September, let it go dormant, mowed it in Feburary and laid down another 6 inches of compost on top - did not till this time. I then laid black plastic on top with hope of killing the cover crop prior to planting trees, shrubs, perennials.

The plastic has been in place now for about 5-6 weeks but it has been cloudy and damp, likely not warm enough to toast those seeds. So, any suggestions as to how to suppress the cover crop from coming up through future plantings?

Someone had suggested using Round-up, wait a week then till everything under, wait two more weeks then plant trees etc., and finally add Surflan. Other suggestions?

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wayne_5 zone 6a Central Indiana

"to toast those seeds."
I don't know if you would toast those seeds under black plastic raised up that far above those seeds. If you mean kill the rye, again the plastic could only keep light out...a slow process perhaps for dormant plants. I guess I would till the stuff up daily until dead.

    Bookmark   March 15, 2012 at 1:26PM
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From your description, it doesn't sound like the cover crop self-seeded. Am I missing something? I'm not a fan of Roundup, but it might be your best bet in this situation. Wait until everything's dead and then til. You should be good to go.

    Bookmark   March 15, 2012 at 2:20PM
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Thanks guys. I sneaked a peak under the plastic and the cover crop, believe it or not, has sprouted through the compost in places. It is rainy now (so can't till) and I'm not sure if Roundup will work until the sun comes out warm for a few days; heaven knows when that will be. Should I leave the plastic down or remove it? That is leaving it down longer won't hurt the soil-food-web will it?

At least I know the ground is fertile!

    Bookmark   March 15, 2012 at 6:00PM
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My vote would be to leave the plastic down and plant through it if need be. If things are sprouting, then you have a viable seed population. If they sprout, but don't get light, they'll die and add to the nutrient base. In a few months you should be able to remove the plastic with no fear of further sprouting, and then finish your landscaping. If you had not already gone to the trouble of buying and laying the plastic, I would have planted my landscaping materials as the season warranted and done a weekly cultivating regime to make sure everything was killed back. Clear plastic is a better choice for heat killing seedlings, but it is probably still too early in the season to rely on enough sun for that treatment to be effective.

    Bookmark   March 15, 2012 at 10:07PM
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I have not found it necessary to cover any of my cover/green manure crops with plastic to "kill" them and since I did not want to "kill" them I would not have done it anyway. Mowing the crop, and then tilling it in has been enough. No plastic. No poisons. No anything that might possibly be detrimental to the Soil Food Web that would work on that cover/green manure crop.

    Bookmark   March 16, 2012 at 7:24AM
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kimmsr is right & has done this a lot longer then I.
I would not use round-up just to kill a annual rye grass.
Just till it under.
Mulch the bed if & when the rye comes up & it will die & rot into compost.

    Bookmark   March 17, 2012 at 2:51PM
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