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Nothing good comes from mulch volcanoes


With glorious weather returning, many gardeners, like myself, are putting down fresh layers of mulch. It is roughly the equivalent of applying a fresh coat of paint in the house. Like paint, there’s a variety of mulch colors available. It is an easy way to make the landscape look great. The big home improvement stores have had bagged mulch on sale the last couple of weeks. Gardeners have also stocked up, waiting for that first nice weekend. But you can get a little overzealous in your mulching habits. Not all mulching is the same.

Over-mulching of landscape trees is perhaps the most visual instance of over-fertilizing, creating what are commonly called “mulch volcanoes.” When a thick layer of mulch is spread around the trunk of a tree, many things can happen, and they’re all bad.

A good rule to remember is to always go out with mulch, not up. In other words, spread mulch horizontally and don’t pile it up against the trunk. Use a rake or pull the mulch back away from the trunk by hand. As the mulch is pulled back, contour it to resemble a bowl. This configuration helps collect water and direct it towards the root system of the tree during rain or irrigation.

Proper mulching provides so many great benefits to our landscape planting: It helps maintain soil temperatures, warmer in the winter and cooler in the summer, reduces weed seed germination and soil compaction and adds aesthetic beauty to your landscape beds.

Most gardeners love their trees and shrubs and want to do what they can to help them grow and prosper. But you can kill your trees and shrubs with kindness. There are gardeners who think if 2 to 3 inches are good, then 6 to 10 must be great. Don't do that!

The depth of the mulch layer depends on the plant. Annual bedding plants need only 1 to 2 inches. Woody shrubs and roses are longer term plantings and benefit from 2 to 3 inches. Trees like a thicker layer in the 3- to 4-inch range.

EDITOR’S NOTE: Dr. Gary Bachman is an Extension and research professor of horticulture at the Mississippi State University Coastal Research and Extension Center in Biloxi. He is also the host of the popular Southern Gardening television and radio programs.


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