Using bluegrass as green manure

silkcom(5)February 16, 2012

Is it possible to just use grass as a green manure? I know that grasses are used, but what about normal lawn grass?

Seems like it's a bit easier than removing the grass, and hopefully will keep the nutrients in the soul.

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It is possible, although that can be very expensive, and might not provide the volume of organic matter you might expect. Some, I think misguided, people do recommend using Annual Ryegrass, "Lolium multiflorum", as a good green manure but that can be very "weedy". I don't recall ever seeding any in my yard and it is growing here every year.
I find seed for Winter, Cereal, or Annual, "Secale cereale", Rye (a grain) less expensive then most all grass seeds.

    Bookmark   February 17, 2012 at 6:36AM
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ralleia(z5 Omaha, NE)

I think that what silkcom is referring to is simply composting the existing grasses in the process of preparing a new garden bed. That, rather than intentionally planting more for the purpose of green manuring.

Yes, if you've got the time to wait, it's a perfectly good idea (and less back-breaking!) to turn that grass into green manure. I normally cover the area with overlapping corrugated cardboard or overlapping newspaper (~13 sheets if you are using newspaper to make it thick enough), and then mulch over that wood mulch, dead weeds, leaves, grass clippings, etc.

I've also heard of a technique whereby you use finished compost as a mulch, and then plant within a few days. However if you have any really tough, weedy, rhizomatous grasses (my "lawn" in that area was infested with quackgrass) then unless given a long time to decompose they can fight you for years.

With bluegrass that should not be an issue.

    Bookmark   February 17, 2012 at 8:20AM
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Thanks, that's exactly what I was asking. What do you mean "if you've got the time to wait"? Do i have to wait after I turn it in to plant?

My current plan, as i'm starting my new garden, is to turn the grass into the soil while I double dig it. Then I'm getting a yard of compost (haven't started my compost bin yet), and was planning on working it into the top 8-12 inches as well. But am I supposed to wait if i mix in the grass?

    Bookmark   February 17, 2012 at 9:22AM
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ralleia(z5 Omaha, NE)

If you mix in the grass with the soil as you double-dig, it isn't going to decompose right away. It won't even die right away--chances are you are going to have a lot of clumps of grass and sod that resist breaking apart and that will try to grow still in the soil, interfering with your garden efforts. Even if all the grass died immediately, the process of decomposing temporarily ties up soil nutrients, which isn't the best thing for the plants you intend to put in.

If you want to plant soon, it would be better to strip the sod off and either toss it in the compost pile or use it where you have bare patches.

    Bookmark   February 17, 2012 at 10:18AM
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Thanks, I guess I still have some learning to do with green manure :). I thought I was supposed to just dig it in, and then plant shortly there after.

I'll keep researching, thanks.

    Bookmark   February 17, 2012 at 11:07AM
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ralleia(z5 Omaha, NE)

When using "green manures," two things are required.

1) You must KILL it.
2) It must decompose.

I've read somewhere that a farmer will tell you that the only good cover crop is a dead one.

Here's what my favorite Rodale gardening book "Growing Fruits and Vegetables Organically" has to say about the subject. "Cover crop" is essentially equivalent go "green manure" in this discussion.

If you have to kill off a cover crop before planting your food crops, try mowing it severely, tilling it under or solarizing the plot. Solarizing will not kill the crop if spring temperatures are cool, with night temperatures in the 30 degree F range.

Keep in mind that after you till the cover crop, your soil microbes intensely attack this rich plant material. There is a lag time of at least two weeks during which nitrogen and phosphorous will be tied up by the microbes as they reproduce and process the residues. So wait two to four weeks after mowing or tilling your cover crop before planting main crops.

    Bookmark   February 17, 2012 at 11:26AM
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So digging it into the ground will kill it, and then I just wait 2 to 4 weeks to use it? That's perfect, as I have 2 or 3 weeks til peas :) and more for everything else.

I'm not really tilling the ground, but the grass will be completely under the ground.

    Bookmark   February 17, 2012 at 2:44PM
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Digging it in won't necessarily kill it. Grass is tenacious stuff, it must be buried deep enough that it can't reach sunlight before the plants' store of nutrients is exhausted. Because of this, the plant doesn't actually start to decompose underground until it stops growing. When you do your double-digging, be sure that the sod is completely inverted, forcing the plant to expend energy sending the roots back down and the leaves back up. Be diligent about weeding at least weekly both before and after you seed the bed and you should be fine.

    Bookmark   February 17, 2012 at 4:15PM
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thanks, will do (Was planning on putting them upside down after i break up the soil as much as i can. Also plan on adding the black fabric (really works out well in raised beds) which hopefully will continue the process for me.

But that does raise the point that it will take longer for the grass to die so what maybe 3-5 weeks before planting?

Though also, planting won't need the nitrogen day 1 as much as a week or so in.

    Bookmark   February 17, 2012 at 4:23PM
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