HAMMOND, La. – Piling mulch too deeply around the base of trees can lead to problems, according to an LSU AgCenter expert.
“One of the tendencies in landscapes now is to make piles of mulch – sometimes resembling the shape of a volcano or fire ant mound – around the base of trees,” said AgCenter horticulturist Allen Owings.
Oaks and other trees, especially small flowering trees, such as crape myrtles, are commonly over-mulched in residential landscapes, Owings said.
Mulch should be spread out horizontally instead of piled up vertically, he said. Trees normally should be mulched to a depth of 3 to 4 inches.
It’s important to keep the transition area between the root and the trunk free of mulch. “Do not bury the tops of the roots that flare out from the trunk,” he said.
Owings cites several problems that can result from over-mulching or piling mulch around the base of trees, including:
– Oxygen starvation of shallow roots.
– Dead tissue caused by reduced oxygen exchange.
– Increased fungal and bacterial infections from increased moisture around the trunk.
– Dead stem and trunk tissue caused by heat buildup from mulch decomposition.
– Change in soil acidity.
– Competition for nutrition from microbes in mulch that’s too deep.
– Habitat for rodents, such as moles, voles and shrews along with mice, rats and more that feed on plant tissue.
Owings recommends that Louisiana homeowners and landscapers use pine bark, hardwood chips, pine straw and similar materials.
Excessive mulching around trees is becoming more common. Although the mulch in this photo may not appear excessive, it has buried the root flare in the mulch. Photo by Allen Owings
The LSU AgCenter and the LSU College of Agriculture