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How often should you add mulch? It depends on what kind you use

Question: Maybe you can solve a little disagreement my husband and I have about our landscaping. He says we should be mulching our flower and shrub beds every year, but I think that’s too much. We usually use bark chips, and I feel like they get too thick if we add more of them every year. What do you think — should we add more every year? If so, should we be removing some of the old mulch when we put on the new stuff every spring?

Answer: I’ll start to answer your complicated question with a review of the basics.

Mulch is any material that’s added to the soil’s surface to help suppress weeds, stabilize soil temperatures, moderate soil moisture and improve the garden’s appearance.

In your case, the mulching material is shredded hardwood bark, but mulch also can be compost, mushroom soil, pine chips, pine straw, straw, hay, untreated grass clippings, river rocks, gravel, or any number of other materials.

It’s important to consider which material you’re using before deciding whether or not to add more of it each year. For example, if you’re mulching a path with gravel or river rock, a single application is enough to last a lifetime, but if you’re mulching a vegetable garden with compost, yearly additions are the most beneficial.

That being said, it’s also important to follow a few rules when you’re mulching, no matter what material you’re using.

First, unless you’re mulching a path where no plants are growing, never add more than 2 or 3 inches of mulching materials at any one time. Thick layers of mulch can reduce air circulation to the roots of all plants, even large trees. It also can smother young plants.

When you mulch, be sure the mulch itself never touches the base of any plant. It should remain two to three inches away from whatever plant you’re mulching. This is important to avoid issues with girdling and bark-chewing rodents. Make a “doughnut” of mulch around your trees, shrubs and other plants; do not pile the mulch up to make a “volcano.”

If you follow these rules, and only add the recommended 2 or 3 inches of shredded hardwood bark to your landscape beds, adding a fresh layer of mulch every year is a good idea. Not only because, over time, the old mulch slowly decomposes and its ability to control weeds is reduced, but also because it really spruces up the garden. There’s no need to remove the old mulch before adding new; again, as long as you aren’t adding too much at any given time.

On my property, I add only 1 inch of shredded hardwood mulch to my tree and shrub beds every spring. That way, it isn’t as expensive as a thicker layer, but I still get to reap the benefits of a fresh layer of mulch. In the vegetable garden and flower beds however, I add 2 to 3 inches of leaf compost as mulch every year. I find its lighter texture to be more pleasing to the eye, and because it decomposes fairly quickly, it adds nutrients to the soil and feeds my garden as it breaks down throughout the summer months.

Horticulturist Jessica Walliser co-hosts “The Organic Gardeners” at 7 a.m. Sundays on KDKA Radio with Doug Oster. She is the author of several gardening books, including “Good Bug, Bad Bug.” Her website is jessicawalliser.com.

Send your gardening or landscaping questions to [email protected] or The Good Earth, 503 Martindale St., Third Floor, Pittsburgh, PA 15212.


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