How mulch mulch is too much?

veetaJune 27, 2011

I am expanding my perennial beds and ordered leaf mulch from my county. My math skills were apparently lacking, so I ended up with a lot of mulch! Some resources say to not pile mulch too thickly, so I wanted to poll opinion here.

1) Where I placed the leaf mulch in existing flower beds, I left several inches clear around my plants. How many inches of clearance is recommended?

2) When I ran out of places to put the mulch, I created new beds by first laying down cardboard/paper and then piling the leaf mulch thickly on top. (In some places I ran out of cardboard and just used mulch). This is mostly about 3 inches, but in some places I've got it piled higher. Is there any potential negative effect of this?

I figure I'll add any remaining leaf mulch to my compost pile (I have few trees, so I have a limited amount of leaves for my pile).

Any comments or suggestions?

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1)The common view is that the mulch, whatever it is, shouldn't touch the stems. That is absolutely true for woody plants, not so carved in stone for herbaceous perennials. If I put mulch over my peonies when they're dormant, they'll grow right through the mulch, so they seem to be okay with mulch right up against them. Several inches distance may increase your weeding, so play it by ear - if you have an explosion of weeds, tuck it a little closer to the plant.

2) The cardboard/mulch thing is good; depending on what you put it over, you may have a bit of a problem with the part without the cardboard - the grass could very well grow right through the mulch. If it's not too big an area, I would rake it up and put down newspaper or something to smother the grass, You could put it down over the mulch and mulch over that, too.

I mostly use free wood chips from the tree guys, and I usually put down 4 to 6 inches; if I've got more, I'll dump it on top. It'll be gone in two or three years, so the more the merrier. I do not, however, mulch that deeply by trees or established shrubs. I also make sure that I mulch over soil that is NOT bone dry.

It sounds like you're doing fine; have fun planning your new beds.

    Bookmark   June 27, 2011 at 5:03PM
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It is hard in my area to have too much mulch. The main thing is to be sure the water from the drip irrigation can get through the mulch...largely a matter of letting it drip long enough. You can make mulch from many things if you have a grinder...prunings, leaves, newspaper, cardboard, etc. I will be blogging on this in a couple of days.

Here is a link that might be useful: In the Charamon Garden

    Bookmark   June 27, 2011 at 6:43PM
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rhizo_1 (North AL) zone 7

The recommended layer of mulch is 2 to 4 inches. Frankly, I don't even like to use 4 inches, but probably would do so if it were leaf compost, which decomposes rapidly.

The problems with a too heavy layer of ANYthing over the plant roots have to do with preventing normal gas exchange (in with the oxygen and out with the carbon dioxide) from the soil, inhibiting root cell division and respiration, forcing plant roots to grow into the mulch in order to access oxygen, moisture, and nutrients, inhibition of rainfall and/or irrigation from normal percolation though several inches of mulch to the soil, etc.

Heavy layers of mulch on the soil can create the kind of environment in which the mycelium of decomposing fungi thrive...not IN the soil but in a slick, often hydrophobic mass on top of the soil.

Yes, mulch is sooo beneficial. But piling two year's worth of 'beneficial' in one fell swoop is not doing the plants any favor. Adding mulch should be, at the very least, an annual or semi-annual (2x/yr.) project.

    Bookmark   June 27, 2011 at 10:31PM
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Many sources do state that mulches should not be thicker then about 4 inches which is just about enough to 1) suppress weed growth, 2) aid in soil moisture retention, and 3) aid in keeping the soil cool, depending somewhat on what your mulch material is. I have not seen a problem with using 6 inches of shredded leaves or even wood chips and in my soil the Soil Food Web will digest that mulch by about the middle of August.
Newspaper or cardboard under a mulch layer helps extend what mulch you do have so if you have only enough mulch material for a 2 inch layer, not quite enough mulch to suppress "weed" growth, but is not really needed if you have enough material for a 4 to 6 inch thick mulch.

    Bookmark   June 28, 2011 at 6:25AM
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This is fantastic news--thank you all SO much for the reassurances. After working so hard on this yard and its gardens, I did not want to screw it up! I'll monitor the weed situation and make sure I water well.

    Bookmark   June 28, 2011 at 11:11AM
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I've questions too. I'm guessing how much depends on the mulch and what you are growing? Correct?

I'm trying to use shredded grass clippings and growing vegetables but if I go over just a couple of inches it seems like it keeps any moisture from getting though from rainfall. I can put a batch on a row about 5 inches thick then have noticed when we get a heavy, heavy all day rain. (say a couple of inches) And midway and underneath the mulch is dusty dry. Frustrating.

I want to use grass because I have an abundance, and it is free but it's tricky to say the least.

When I go a deep on mulch it's great at keeping weeds down but no moisture gets through.

    Bookmark   June 28, 2011 at 9:37PM
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rhizo_1 (North AL) zone 7

gnhelton, you're right! Grass clippings, fresh from the lawn, can be a real problem when used as a mulch. My neighbor singlehandedly killed one new ornamental tree after another by heaping her grass clippings on them. My husband and I would sneak over and stir the mess up when she was not at home, but it was never good enough to save them.

Best scenario? Mow often enough so that you can keep the clippings on the lawn where they can do the most good. Talk about free fertilizer! Second best: start a little compost pile with your clippings, a bit of this and a bit of that...keep it stirred up until the clippings are more decomposed.

You can also add just a little sprinkle of the clippings on top of other mulch and it will soon disappear.

    Bookmark   June 28, 2011 at 10:51PM
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Never too much mulch on hand, but can be too much in one place as explained by other posts.

You also can also top up your mulch in fall, but especially in the full sun locations your mulch might need topping off this summer. I just applied more mulch this morning to a spring planted bed in full sun that the 1" applied after planting was gone.

My ground freezes & thaws several times throughout the winter season, so I'm careful not to pile on top of plants, but I can mulch around many with the leaf mulch. Some do better with conifer branches as fall mulch to protect the crowns from winter wet in my area.

Your question was about leaf mulch - is it from last year's shredded leaves & composted into a nice earthy smelling brown? OR newly shredded from fallen trees? There is a difference. The newly shredded green stuff will need to cure a bit & dry out before use or it will be like fresh grass clippings...

You can also bag up the excess (in black plastic, not burlap), put in an out of the way place, & save for starting seeds next spring as leaf mold. If truly just shredded leaves they will compost in the bags & be weed-free for you! I try to stash as many as I can & use the black gold everywhere in spring. Any extra can be used to build a huge compost pile in spring with all those extra green grass clippings when you have a shortage of browns to go with!

Extra can be piled more thickly in paths, away from drip line of shrubs & trees, etc. Can cover with burlap or plastic to keep weed free for application in fall or when you are digging out & dividing to fill the holes back in.

I love the tip about using a bulb planter to dig a hole where you want groundcover, then go to groundcover & use bulb planter to dig out a section, go back to the 1st hole & unload your groundcover, then go back to the other hole & fill with compost. Sounds more complicated than it is & you can do it in summer if kept moist (use more mulch!)

I have spare mulch, but never too much because I end up using all my stashes in one season or another. Just be careful around stems of plants & you'll be happy with "too much mulch around".

I even mulch potted plants in summer.

    Bookmark   June 30, 2011 at 6:27PM
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Ruth Stout didn't think there could be too much mulch! She used hay, which I have done this year. It works quite well. This is permanent and I plant right into it and add more when necessary.

    Bookmark   September 18, 2011 at 5:56AM
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If the mulch you put down is to 1) aid in suppressing "weed" growth, 2) aid in retaining soil moisture, 3) aid in maintaining a steady soil temperature, and 4) add organic matter to the soil then the mulch needs to be thick enough to do that and an inch or two will not be. Mulches less than 2 inches thick can allow enough sunlight to reach the soil to encourage "weed" seed germination and growth.

    Bookmark   September 18, 2011 at 6:47AM
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