Mulch in Moderation

Apr. 2nd, 2018 by W Scott McAdam Jr.

When it comes to mulch, the temptation is to do too much—packing 6 to 12 inches of mulch at the base of a tree. It’s called a “mulch volcano,” the landscaping equivalent of issuing a slow, but sure, death sentence.

When done properly, mulching can be a great asset for a landscape. But a variety of problems erupt from mulch volcanoes, including:

  1. Rot – the bark at the base of the tree can begin to decay and rot because the mulch maintains a dark, moist environment. This can promote insect activity and is also a breeding ground for fungal activity.
  2. If the pile is large enough, it can begin to compost, which generates heat. That heat can damage the cambium (inner bark) of juvenile trees.
  3. Secondary rooting can occur in the mulch, rather than in the soil. By rooting out of the soil, these roots can begin to wrap around the base of the tree and girdle the trunk, or larger roots, over time. 

The solution: mulch in moderation—about a three-inch layer is ideal.

Special thanks to one of our valued ATPE readers, Ann, who suggested this topic. If you have a question or idea for a future Ask the Plant Expert, contact me at

This installment of "Ask the Plant Expert" will be published in the April 4, 2018 edition of the Wednesday Journal of Oak Park and River Forest, the Forest Park Review and the Riverside-Brookfield Landmark.