Hill Gardens of Maine - Perils of a Mulch "Volcano"

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Perils of a Mulch "Volcano"
by Fred Davis, MG, Hill Gardens of Maine (To view other articles, click Archives)

Welcome through Fred's Garden Gate! Mulch Volcanoes — an unnecessarily tall cone of bark, sawdust, or shredded leaves placed around newly planted landscape trees — is fraught with serious, even fatal, consequences. Most of us have witnessed this oft-unrecognized error. Trees that, even though they were healthy when first planted, never truly prospered, and exhibited dramatic symptoms of severe drought stress — even death. Trees that have been severely damaged by "girdling" by small rodents. Trees that should be literally exploding into strong, healthy, and luxurious growth...but are not.

Don’t misunderstand. Mulching newly planted trees is a good idea. Properly applied mulch conserves moisture, moderates soil temperature, discourages weed growth, and generally adds an attractive appearance. But when applied incorrectly, well. . .that’s a horse of a different color!

This time we’ll look at several of the most critical dangers faced by a great many gardeners — even landscapers-for-hire — when mulch is applied incorrectly.

First and foremost, tall, cone-shaped mulches "shed" water (arriving either naturally through rain, or by supplemental irrigation or sprinkling) in much the same way an umbrella keeps the user dry. That’s because the surface of mulch quickly dries, inhibiting the passage of water. When that mulch is domed up, water simply runs off and ends up well outside the limited range of thirsty roots. In later years, that wouldn’t necessarily be a problem but, for the first year or two after planting, new trees must rely entirely on water that actually reaches the original (usually round and compact) root ball that came from the nursery. Trees trying to exist in such conditions quickly perish.

Nearly as critical, if mulches are applied in the four- to six-inch-deep range, newly developing tree feeder roots actually migrate up into the mulch rather than down into deeper soil. It’s easy to see that the first time a gardener forgets to water, or it doesn’t rain for several days — even if water could soak into a mulch volcano — our tree will suffer from more severe drought than if no mulch had been applied at all. Additionally, deeper roots in the ball may actually suffocate because of now being buried too deep by an extra several inches of mulch.

As if that isn’t enough to spell disaster and severe stress for the new tree, deep mulch — especially in a volcano (cone) shape — provides comfortable and dry winter quarters for bark-nibbling rodents. And we all know what happens when mice, shrews, voles, or other furry critters chew away large sections of bark. Right! No bark means no movement of sap or nutrients to the upper branches, leaves, flowers and seeds. Certain death.

Deep, volcano-shape mulches very often set up perfect conditions for the formation and growth of fungal cankers or other tree bark diseases.

So, how should mulches be applied around landscape trees and shrubs? Mother Nature, in her infinite wisdom knows! She’s developed the perfect system for mulching. Leaves naturally fall from trees in a more or less even layer; they rarely form deep mounds at the base of trees; and they are leaves. . . never tall piles of artificial-looking shredded bark, sawdust, or peatmoss.

Those 1 1/2 to 2 inches of fallen leaves in nature slowly decay, eventually becoming an important element in the long-term nutrition of the soil those trees live in. Mother Nature never creates mulch volcanoes around trees. And we all know how rapidly most woodland trees grow and, generally, how healthy, durable, and resistant to disease and insect damage they are.

Besides, an annual two-inch layer of shredded leaves in a circle about three feet wide all around newly planted trees and shrubs is infinitely more attractive — and more efficient — than unnatural, deep volcano-like cones of freshly shredded bark or bark nuggets from the big-box-stores or other questionable sources. Shredded leaves are rarely accompanied by packaged ant nests or the presence of highly objectionable weeds like horsetail and crabgrass!

Do yourself a financial favor: the next time you purchase and plant an expensive tree or shrub, give it the best shot at life and prosperity that you can, and that it deserves. Lay down a flat or only slightly mounded two-inch layer of Nature’s mulch — shredded leaves. And ensure that it receives ample water around the root ball. The end result will look a whole lot better than a stressed-out, half-dead snag "erupting" from a mulch volcano!

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