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ben harpo
Posts: 76
Location: Illinois, zone 6b
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Is it OK to spread fresh grass clippings as mulch on top of a garden?

During my first internship I was told that cover crops have to be rolled in two weeks before planting because the fresh stuff ties up nutrients and inhibits germination. However, I am doing most of my germination in soil blocks and transplanting out. Once the crops are rooted in good, is there still a problem with adding green mulch on top?

There is a cemetery adjacent to my property with grass mowed regularly. I can rake it up for free. I might haul it using garbage bags and a hand cart. The garbage bags will initiate a fermentation process. Don't know if this is good or bad?

Also I could make the grass clippings into a stack to cure and spread it on the garden two weeks later. Any thoughts on the best way to handle this phase of it are appreciated. Thanks.



 
John Elliott
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Cut grass is problematic as mulch. After a heavy rain, it can pack down and keep air from getting to the soil. All those slick pieces of grass sticking together isn't good, and if it stays that way for a while, it can lead to anaerobic conditions under the mulch. Besides killing off beneficial soil fungi, anaerobic conditions are bad for plants as well.

If you can mix it with wood chips or leaves or some other material that has different shapes from the grass blades, that will help. Letting it "cure" for a couple of weeks is also a good idea. Once the grass dries out, it is less likely to stick together and turn into an impervious mat during a rain.
 
Su Ba
pollinator
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Location: Big Island, Hawaii (2300' elevation, 60" avg. annual rainfall, temp range 55-80 degrees F)
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I use grass clippings as my primary mulch. I apply them fresh cut if I can. My method is to apply a thin fluffy layer, about 2 inches thick. I don't stamp them down. I leave them fluffy, just as they are as I spread them around. The sun and air dries them enough so that they don't make a gooey, slick layer. I want to avoid that slick layer. The clippings will dry out so that the layer shrinks to 1/2 to 1 inch thick. If and when to soil shows through, I add another layer of grass clippings. Time wise, that could be as short as one week or as long as a month. Around potatoes and leeks I don't wait to see the soil surface peeking through. For these two crops I add more mulch weekly or every other week.

If I store the clippings in a pile or a trashcan overnight, they will heat up. I can still use them for mulch, but I avoid putting the hot clippings next to plants. The heat can damage or even kill delicate vegetation.

If I leave the pile of clippings sit too long, it gets soggy and gooey. I don't discard them at this stage, but I'll use them atop some persistent weed or grass clump that doesn't want to give up. Or use them atop cardboard where I'm trying to kill the sod.

So basically, I use grass clippings fresh and don't apply them too thickly. I apply enough to keep the soil covered. They are my number mulching item. I have a lawn tractor with grass catcher bags. And I have access to almost ten acres of grass that I can use to harvest grass clippings from. Between the various gardens, orchards, grow boxes, etc of my farms, I use every drop of those clippings!
 
Su Ba
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I received two purple mooseages from different people, one warning me that using grass clippings will result in disaster (per a permie course) and another asking me why grass clippings work for me because she had been warned not to use them. So rather than keep my answer private, I've decided to answer publicly.

Perhaps clippings work for a few reasons.
1- The clippings are rather coarse, since the grasses are pasture grass rather than fine leafed front yard lawns. In the past I have used lawn clippings, but I applied them thinly so to avoid that clumpy, gooey problem. Years ago I had success using lawn clippings. I would use them today if that was what I had available.
2- Apply thinly and fluffy so that they can dry. They will mat somewhat with time, but not to that gooey black muck, which is to be avoided.
3- Gradually built up the depth of the mulch for crops needing good light protection, such as potatoes and leeks. I've built up mulch to 7-9 inches for such crops.
4- Apply to plants that are growing large enough not to get covered with the mulch. I don't apply clippings to small stuff like baby beets that will get smothered when a breeze blows the clippings over them. I wait until plants are larger.

I was warned that clippings would rob my soil of nitrogen. I haven't found that to be the case with clippings laying atop the soil as a mulch. My soil hosts a decent population of soil micro organisms, which perhaps prevents that problem. A part of keeping the soil "alive" is keeping it moist and the direct sunlight off, both of which can be accomplished via the clippings mulch.

I was warned that tilling in the old mulch would bind up soil nitrogen. But again, my soil is host to various soil micro organisms and worms. And I don't till in fresh clippings. I have not see nitrogen depravation in my crops. Plus I don't till in excessive amounts of mulch, like that found on my potatoes and leeks. The excess mulch is moved to other crops before tilling.

I was warned that grass clippings mulch would prevent rain from reaching the soil. Again, I have not seen that. I apply mulch fairly thin, keeping it about 2 inches thick in most cases. Importantly I apply mulch to already moist soil, NOT dry soil. I find that my mulch helps keep the soil moist but reducing evaporation due to sun and wind. Yes, a light rain may not penetrate the mulch, but it still will help keep the soil from drying out. Heavier rains definitely get through my grass mulch.

I hope this answers the questions raised.
 
ben harpo
Posts: 76
Location: Illinois, zone 6b
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The way I've always made hay is to cut in the afternoon, rake around noon the next day, bale the day after that. It seems to keep forever without turning into goo. Granted that is different than lawn clippings. Lawn clippings probably have higher nitrogen than hay because in grazing school they teach that most of the protein is in the tip of the vegetative grass. When I roll down legumes they seem to always get gooey. I'm going to try using the grass clippings, I'm just looking for suggestions on how to handle it.

In the book Farmers of Forty Centuries by F.H. King it describes how the Chinese applied fresh green manure to all sorts of crops. Most commonly their fields had sunken paths and the farmers would trample the green manure into these wet paths. This would seem to create impermeable mats of goo deliberately. But at least the paths were some distance from the base of their plants.

The nutrient tie up is supposedly due to an explosion of soil microbe population digesting all the fresh nutrients in green manure. Similar to the algae blooms in the ocean that go crazy on phosphorus and nitrogen, but tie up oxygen in the process. At least that's how I've made sense out of all the things I've heard, I'm no expert on this.

What is the problem with adding mulch on top of dry soil? I've done that, and after time the soil underneath is very moist. I've even cultivated with a hoe to get rid of all the insurgent weeds and mulched a few days later on top of the hot dry pulverized soil. The results were very good.
 
Su Ba
pollinator
Posts: 978
Location: Big Island, Hawaii (2300' elevation, 60" avg. annual rainfall, temp range 55-80 degrees F)
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<<<What is the problem with adding mulch on top of dry soil? >>>. In my location, I may not have rain showers over 0.1" for months on end. Then I'll get 4"-6" of rain over night. Then again I could go a number of months till the next good rain. Therefore I find that a new garden bed gets a better jump start by being wet before applying my mulch. That way it will still benefit from our 0.1" showers.

So it just goes to show you that gardening methods vary greatly from one region to another!
 
ben harpo
Posts: 76
Location: Illinois, zone 6b
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Mulch catches a lot more dew than bare soil. And it stops surface evaporation. A lot of water moves up from underground due to capillary action.
 
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