Mulch Volcanoes: A Good Way to Kill a Tree
Mike Mickelbart, Assistant Professor, Department of Horticulture
& Landscape Architecture, Purdue Univ.
Janna Beckerman, Assistant Professor, Department
of Botany & Plant Pathology, Purdue Univ.
Spring is a time for planting and re-applying
mulch to beds. A common mistake with respect to these activities
is applying mulch too high around the trunks of trees and shrubs.
This mistake results in what looks like “mulch volcanoes.” When
mulch is in contact with tree trunks for long periods of time,
bark decay can occur. Another possible effect of the mulch volcano
is rodent damage because rodents can nest in the mulch and have
direct contact with the trunk. When mulch is applied as a 4 to
6 inch layer, feeder roots can grow into the thick layer mulch.
Those roots are much more susceptible to water stress during dry
periods than roots that are below the soil surface.
A sure sign of improper mulching is the lack of
a transition area where the tree trunk flares above the soil surface.
Instead, the tree will look like a telephone pole sticking out
of the ground. Mulch should be applied in a donut shape around
trees, and not more than 2 to 3 inches thin to avoid these potential
Photos courtesy of Janna Beckerman