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As a public service announcement and as a way to positively contribute to the urban forest, this article by Kathy Thomas of Green Thumb landscaping pleads for people to stop mounding up mulch around tree bases. If you’ve been on Tenth Avenue between Cambie and Oak Street recently, you will have seen such mounding up.
As Ms. Thomas notes “In recent years, these mounds of mulch have become as prevalent as the bubonic plague in 14th century Europe. Why individuals continue to believe that eight to 12 inches of mulch piled around a tree trunk is a good idea remains unclear, but the fact of the matter is they’ve sentenced the plant to a slow death.
These issues have been on-going, but in recent years people have started to mound mulch up around the base of the trees – the ‘mulch volcano,’” said Martha Smith, a University of Illinois Extension horticulture educator. “New problems have emerged because of this practice. Tree bark is meant to protect the trunk. It works best in the air and light. If you pile mulch onto the bark, it is now exposed to dark and moisture. Bark will begin to rot, and rotted bark cannot protect the tree from insects and diseases. In fact, diseases grow better in this type of environment.”
Don’t get me wrong-mulch has good things about it, but needs to be used in moderation. That means spreading the mulch around the tree base, not making a mulch volcano at the tree trunk. Those volcanos create heat at the trunk that can kill inner bark, and promote secondary roots in the soil, which can girdle the tree’s main roots. Instead leave mulch about two or four inches around the base.
An important factor to keep in mind is that while mulch is aesthetically pleasing, the attractive color tends to fade but this doesn’t mean you should top off the organic matter with a couple of inches of fresh material. Measure the mulch levels before deciding to add more or you can end up smothering the tree despite your best intentions…Education about this ill-informed practice will perhaps eventually make these mulch volcanoes go extinct.”