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Illinois Country Living

David Robson Extension Educator, Springfield Extension Center, University of Illinois

Yard & Garden

Much to do about mulch
How to conserve water, control weeds and avoid slime mold

Last month, talking about water conservation, the word “mulch” was used at the end of the article. Of course, mulch is a good word, if used correctly. Occasionally, mulch becomes something less than positive.

First the negatives.

Sometimes mulch goes where you don’t want it, especially in the fall when you’re using a leaf blower to move leaves. The mulch sometimes gets repositioned as well, leaving the soil exposed.

Mulch isn’t permanent. While this can be a good thing as we’ll see below, it’s annoying to have to go out each spring and buy more. Of course, some buy more just to put down a fresh layer for the look.

Fresh mulch, however, can be a source of slime mold, one of those conditions that almost keep people like me employed.

Slime mold, to be blunt, and my apologies if you are eating breakfast or lunch while reading this, looks like dog vomit. It sort of has this chunky white to yellow color, but tends to be more solid and doesn’t smell.

Slime molds occur because a fungus grows on the fresh wood pulp, especially if the mulch is kept thick and there is little air movement. And when you look at where and how wood chips are applied, you can get an idea how slime mold seems to develop overnight.

Slime molds are almost like flies and Asian lady bugs – more annoying than problematic. Slime molds don’t affect the plants or the mulch. They just look bad. In most cases, you can take a hoe or rake to them, and that’s it. Of course, if the mold is dry, you might spread the spores, but just keep the mulch on the drier side (if it rains, you have no control), fluff it up every now and then with a rake, and make sure the wood chips are slightly decomposed.

In other words, while free wood chips from the municipalities, parks, tree trimmers and utility companies are a great source of mulch, the wood might be too fresh. Compost it a year behind your garage and it won’t grow the slime molds.

Now, the positives.

Mulch is a great way to control weeds, keep the soil cool, and limit how much water you need to apply by limiting soil evaporation.

As mentioned above, organic mulches such as wood chips, bark, cocoa bean hulls, grass clippings, leaf mold (partially decayed leaves) or compost will break down over time, improving the quality of the soil. However, don’t expect a miraculous soil improvement overnight or even within decades or centuries under trees and shrubs. Since you aren’t actually pushing the mulch down deep, it really is only affecting the top inches.

Mulch that breaks down and is dug in deeper in a flower or vegetable garden has a better chance of improving the soil.

With most mulches, use 2 to 4 inches during the summer. (Use only an inch or less of cocoa bean hulls; otherwise white mold grows on it.) That’s enough to keep down the weeds and keep in the moisture. Once you start getting deeper levels, it’s harder for rain or irrigation water to reach the soil. Air exchange is also limited.

Two to four inches also won’t attract termites, as the mulch dries out too fast and won’t create a humid environment that termites need.

Some mulches, such as compost, grass clippings and leaf mold, break down much faster than wood chips and bark. You may have to reapply more often to maintain the 2 to 4 inch level.

Over the years, it’s amazing to see what people call 2 to 4 inches. Take this magazine and fold it in half longwise. That’s 4 inches. Do it again and that’s two inches. However, if you are going to use this magazine as a measurement, use old issues.

More Information:

David Robson is an Extension Educator, Horticulture, at the Springfield Extension Center, University of Illinois Extension, P.O. Box 8199, Springfield, IL 62791. Telephone: 217-782-6515.


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