P&PDL Picture of the Week for
May 1, 2006

Mulch Volcanoes

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 problems.

Photos courtesy of Janna Beckerman

Click image to enlarge

Volcano mulch around tree

Volcano mulch around tree

Purdue Plant & Pest Diagnostic Lab Purdue Cooperative Extension Service