A 'volcano' of mulch against trunk will slowly kill an old or new tree
Question: Is it a good gardening practice to pile soil or mulch up around the bottom of trees, many times to a foot or more in height? I always thought that practice, along with stripping the bark off the tree with a weed whacker, would surely kill a tree, but lately I've been seeing it everywhere. Am I wrong?
Answer: You are absolutely right! This is one of my horticultural pet-peeves, and I have a hard time not jumping out of my car and removing the mound of mulch every time I see it. And, I see it almost every day, in parking lots, at private homes and in front of various businesses.
Creating mounds of mulch around trees results in a slow, but certain, death for the tree.
It's unfortunate that so many landscaping companies and homeowners still conduct this harmful practice, perhaps thinking they are helping the tree by adding extra mulch.
Trees whose trunks are enveloped in a thick layer of mulch will show signs of decline within a year or two. It may start with branch dieback and then progress to peeling bark, or vice versa. It make take many years for the tree to die completely, but if the trunk's base is continually smothered by mulch, death is inevitable.
Piles of mulch against the trunk also promote damage from bark-chewing rabbits and rodents who enjoy nestling underneath the mulch, especially during the winter months.
Whether it's a newly planted tree or an old, established specimen, the proper way to mulch a tree is to create a doughnut of mulch around the base of the trunk, not a volcano of mulch piled against it.
The base of every tree trunk flares out slightly just before the root system begins. This root flare should always remain above the soil or mulch line. The root flare should never be buried under the ground or smothered in mulch.
Trees are best mulched with a layer of shredded bark no thicker than 3 inches deep. Heavier applications of mulch may prevent air movement through the soil to the tree's roots and eventually lead to reduced growth and vigor, and perhaps, death.
You also are correct in saying that weed whackers can easily damage trees. Because water and nutrients are transported in the tissue just beneath a tree's bark, if repeated weed whacker damage eventually removes all the bark from the full circumference of the base of a tree, the tree will die.
Protect the base of trees from weed whackers and mowers by not allowing grass or weeds to grow against tree trunks or by being extremely careful to keep the string or blade of the weed whacker away from the tree's bark.
Horticulturist Jessica Walliser co-hosts “The Organic Gardeners” at 7 a.m. Sundays on KDKA Radio with Doug Oster. Send your gardening or landscaping questions to tribliving@tribweb.com or The Good Earth, 503 Martindale St., Third Floor, Pittsburgh, PA 15212.
