A mulch ‘volcano’ is a thick mound of mulch piled up around the trunk of a tree. You see them all over — in public parks, private yards and commercial landscapes.

The problem is that mulch volcanoes can kill trees, especially newly planted trees.

Tree bark needs air circulation. Deep mulch suffocates root balls by cutting off oxygen from the base of the tree. In deep mulch the roots will grow up into the mulch seeking oxygen rather than out away from the tree. These roots can girdle and strangle the trunk.

A large-domed mulch pile sheds water instead of letting rain or irrigation water seep into the tree’s root ball. It is better to have an indentation around the tree to collect water.

And, while mulch volcanoes shed water, they also hold moisture that softens the bark and causes fungus and rot. Insects and rodents burrow in deep mulch piles. If a rodent chews the outer bark, the protective layer of the tree is gone and the tree will die.

Proper Mulching for Trees

Image by The Conservation Foundation

Proper mulching, on the other hand, is good for trees. Mulch should be no more than 2 or 3 inches deep and should not touch the bark. Spread mulch out from the trunk for a minimum of two feet or as far as the drip edge of the tree.

A mulch ring around a tree provides protection from mowers and trimmers. It will help the root ball retain moisture and moderate the soil temperature. Proper mulching also controls weeds, and reduces soil compaction from mowing equipment. When mulch decomposes, it provides nutrients to the tree.

Spread the word. Help our trees live long healthy lives.

By Ellie Goldberg, www.healthy-kids.info and Beth Schroeder, Schroeder Design