Wednesday, September 21, 2011

Killer Mulch

Lately, I've been amazed and disheartened to notice how many trees die of mulch. That's right: mulch.

With extreme-weather events growing more and more prevalent, landscape trees and shrubs must contend with hurricanes, tornadoes, ice storms, droughts, wildfires, flooding, lightning...sometimes it's like a war zone out there.

But since mulch has become a decorative addition to many landscapes, surpassing its purely functional purpose of the past, what should be a benefit to plants is increasingly becoming an outright killer. The problem is with "coning"—piling mulch in a deep cone shape against the trunk.

You've seen this practice for years in shopping-mall landscapes. Now it's becoming a common sight in residential landscapes.

Coning puts a plant at risk in three ways. First, piling mulch around the trunk can cause trunk rot. Second, mulch that is piled deeper than four inches can suffocate roots, especially those of young transplants. And third, new roots can grow directly into these mulch cones—then, because mulch dries faster than soil, those roots are quick to die during drought conditions.

To prevent this from occurring, keep mulch at least a foot away from the trunk, and limit it to four inches deep. Use light materials, such as cedar mulch, to promote air circulation (yes, roots do "breathe"). And pull mulch materials back altogether during persistent wet spells.

Landscape plants are threatened enough by extreme-weather events. It's downright painful to think of them dying because of what was intended as an act of kindness.

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