I always add mulch to my trees to help retain moisture, but according to landscaping experts, I’ve been doing it all wrong. Instead of promoting growth, it’s causing them harm.
While mulching in general is good for your garden, according to The University of Maryland Extension Home and Garden Information Center, “mulch volcanoes” can do more harm than good. A recent YouTube video shared by the University explains how this common habit is becoming an “an epidemic in landscaping.”
What is a mulch volcano?
Mulch is good for your garden, and it’s one regular job we’re all encouraged to do to promote healthy plants.
“The purpose of mulch is to help retain moisture, limit growth of weeds, and provide a natural source of micronutrients and other organic matter as the mulch breaks down,” explains Kaustubh Deo, president at Blooma Tree Experts.
However, the issue arises when the mulch is piled up like a volcano into a cone shape around the base of the tree trunk. And it’s a classic mistake that Deo sees homeowners and landscapers making when caring for trees.
Poorly applied mulch can lead to tree death
“The primary issue is that it retains moisture against the base of the tree, which can create fungal issues, decay, or other rot — we don’t want the moisture trapped against the tree bark, we want it trapped in the ground where the roots can access it,” he says.
Instead of improving the health of the tree, it can work in reverse. “Poorly applied mulch can lead to tree death, which is a sad outcome given most people are applying mulch to help their trees!” Deo adds.
What harm does a mulch volcano cause in landscaping?
While applying mulch around trees isn’t necessarily bad, it causes a problem when applied in a mound and prevents airflow from reaching the ground.
“Constant piling means that no oxygen is reaching the plant roots and can be slowly suffocated over a prolonged period,” says Chrissie Handley, lawn care and gardening expert at Online Turf.
She adds, “No airflow and constant retained moisture is also the perfect environment for root rot, causing your tree to slowly die.”
Apart from causing root suffocation, Edwin Dysinger at Seedtime says the lack of oxygen stresses the tree and inhibits its growth and soil biology. He also explains that root girdling occurs, stating, “A heavy mulch can cause tree roots to grow in circles around the tree rather than out from it.”
What’s more, deep mulch can also cause the roots to remain shallow, near the surface, or even grow in the mulch. “This weakens the tree’s attachment to the earth, making it more susceptible to falling over in high winds,” he says.
A heavy layering of decaying mulch can also attract pests, such as rodents, insects and fungi, which Dysinger explains will damage the bark and underlying wood.
The best way to mulch trees
Although it’s not advised to use the volcano mulching technique around tree roots, mulching the roots still remains a good practice.
“Instead of mulch volcanoes, spread woodchips at a depth of 3-6 inches around the base of the tree, but leave a 4-6 inch gap from the base of the tree. Think donut, not volcano,” says Basil Camu, arborist and founder at Leaf & Limb.
Think donut, not volcano
However, Dysinger is more conservative and recommends keeping the mulch depth to no more than 4 inches, as otherwise you run the risk of causing root suffocation and girdling.
There are many benefits to growing trees in your yard, including improved mental health. Additionally, trees attract an abundance of wildlife and are popular with birds. Plus, even with limited space, you can find plenty of small trees suitable for compact yards.
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