Is it always best to mulch?

slowpoke_gardenerApril 21, 2014

I seldom mulch cole crops except close to harvest, and that is done to help keep the soil from splashing on them (wife hates gritty greens). This year I tried mulching some broccoli and cabbage before the last cold spell. The south garden I mulched and the north garden was not mulched. You can see the south garden was damaged much worse. There is at most 150' between these two gardens, neither one is protected in any way.
I think the mulch insulated the ground and did not let the much needed heat radiate up and protect the plants. (The tomato plants were planted today and were not exposed to the cold weather.)

This is the north garden.

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Okiedawn OK Zone 7

I don't know if it is always best to mulch, but it normally is a good idea to mulch. I usually put on only a thin layer (about a half-inch thick) of mulch in February through late March or early April, depending on the weather, because I don't want to keep the soil so well-insulated that it cannot heat up. Sometimes I don't mulch at all until at least mid-April. Once I feel like the worst of the cold is behind us, then I pile on more mulch regularly until it is about 3-4" thick by June. I rely on the mulch to keep the weeds down, to maintain soil moisture and to keep the soil cool in summer.

In late winter/early spring I would rather not mulch at all so the soil can warm up as much as possible, but without a thin layer of mulch the veggie and flower beds start sprouting weeds.

Sometimes there is an exception---I mulched the onions heavily when temperatures in the 20/teens threatened them, but then raked back the mulch a little farther away from them after that severe cold spell passed.

I think your assessment of why one bed had cold damage and the other one didn't have damage likely is exactly what happened. It is hard to be sure, though. I've seen a broccoli or cabbage plant suffer severe cold damage on an exceptionally cold night while an identical plant of the exact same variety right beside it wasn't damaged at all. Sometimes stuff just happens and we can't explain why.

    Bookmark   April 21, 2014 at 2:47PM
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Dawn, thanks for your response.

    Bookmark   April 21, 2014 at 5:06PM
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sand_mueller(z 7a, oklahoma)

You don't really want mulch down when its too wet, although that hasn't been much of a problem lately.

    Bookmark   April 21, 2014 at 6:04PM
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Do you mind if I ask a question here? I haven't wanted to start a new thread about mulch.

Is it sometimes bad to mulch (with prairie hay) because of potential thermal heat? For example, my wheat and alfalfa (growth) when they are very young. If I water atop the mulch can thermal heat a problem?

    Bookmark   April 21, 2014 at 7:23PM
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I love hay except for the seeds in it. I never use fresh hay, and I don't mulch deep. I use more leaves than anything else. The shredded leaves sort of have a shingle effect and the water is a little slower going through it, but I expect that works both ways and the water will evaporate a little slower through them also. The only thing I have heat from is grass clippings, I let them dry and only use a very thin layer of them. I have noticed that the oak shavings I use around the edge of the garden will be damp down in the pile, while the pile of leaves will be dry after an inch or two down in the pile.

    Bookmark   April 21, 2014 at 9:01PM
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I always use fresh grass clippings to mulch with, I put it on about 3-4 inches deep, I never have a problem with it an it makes excellent compost for the garden.

    Bookmark   April 21, 2014 at 9:09PM
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Okiedawn OK Zone 7

Larry, You're welcome.

Bon, I don't know how to answer your question because so many variables are involved. Much would depend on how dry or wet your ground and mulch both were at the same time.

I've never had a thermal heat issue, but then my area tends to be dry most of the time, so my mulch is dry a lot more often than it is wet. If the ground is soggy, I'm not mulching anyway because it is too wet to cut the grass and I don't have grass clippings to use as mulch if we aren't mowing. I'm not wetting my mulch with a hose or sprinkler because the drip irrigation lines drip the water down beneath the emitters, so my grass clipping, hay, straw and chopped/shredded leaf mulch is mostly dry.

Our garden is so large that no one area gets too much new mulch piled on top of the old mulch at one time. If each bed gets a half-inch of grass clippings added per week, we're having a pretty good year. My mulch usually stays so dry that it doesn't decompose into compost until the following year. This past year was so dry that the mulch on most of the raised beds didn't even decompose over the winter....that mulch was just sitting there as dry grass clippings when it was time to rototill the mulch into the soil in order to plant this spring's crops.

If I am too busy with something else to use the grass clippings immediately, Tim dumps them from the mower's grass catcher into a large child's wading pool. Sometimes, by the time he is done, the grass is piled up in that pool about waist-high. If there has been any recent rain, and if there's some leaves or other carbon source mixed in with those grass clippings, the middle of the pile can heat up fast and begin decomposing quickly---within a few days. If it takes me a week to get around to using those clippings as mulch, they often are very hot and partially decomposed when I take them out of the wading pool and haul them, one wheelbarrow load at a time, to the garden. You'd think they were so hot that they'd harm the plants through thermal heat, but they don't. However, I'm only adding a thin layer to the already-existing mulch. If I was laying them on thicker, the clippings might create too much heat.

Last week Tim dumped grass clippings mixed with some chopped up autumn leaves into the wading pool on, hmmm....probably Tuesday evening. Today I used them to mulch newly planted tomato plants and those clippings were already so hot in the middle of the pile that they were decomposing. Since I spread them out so thin, I wasn't worried about the heat. If I'd been planning to put a thick layer of them somewhere today, I would have ditched that plan and spread them out and let them dry and cool down before using them.

I think you'll just have to try it and see what works for you. I think our plants are so hot from ordinary Oklahoma heat and sunlight that the thermal gain from fresh clippings doesn't even faze them.

I will add that I never fertilize our lawn so am not putting a lot of extra nitrogen on the grass. If someone regularly fertilizes their lawn, their clippings may get pretty hot and provide more thermal heat than their plants would like.

For what it is worth, I've tried to smother bermuda grass and Johnson grass with 2 or 3 feet of fresh grass clippings piled on top of the grass in the dead of summer.. I was hoping the thermal heat gain would cook their roots and stolons. It didn't.


    Bookmark   April 22, 2014 at 12:16AM
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We recently tried drowning the bermuda roots. Amazingly, some roots were thriving. Placing the roots exposed directly to the sun for complete drying is the only sure way to kill the darned things! It seems to take an enormous amount of greens to compost them, so I'm just burying those certain to be completely dead.

When I piled the mulch on some alfalfa sprouts and, then, wheat and came back a few days later to water from atop the mulch I considered the 30:10 rule of browns and greens. The hay was 20 to 30 and the new sprouts about 10. I wondered if caution is due.

It would be better to leave the soaker hoses beneath the mulch, but I only have one and move it around.

    Bookmark   April 22, 2014 at 2:44AM
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