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Ask a Master Gardener: Mulch Volcanoes or How to Kill Your Trees

By Alice Marty, Mobile County Master Gardener, www.mobilecountymastergardeners.org

A new landscape trend seems to be in mode around town. It can be seen at homes, businesses, and even schools. Mulch volcanoes are popping up and beginning their quest to slowly kill your trees. It is a very slow death, taking years to complete.


What is a mulch volcano? It is simply an overabundance of mulch piled around and against a tree or other woody plants in a volcano-like shape. Research from UF/IFAS (University of Florida), as well as the ISA (International Society of Arboriculture) consistently recommends against the practice of volcano mulching.

Why is a mulch volcano a bad thing? · The mulch volcano holds moisture against the tree trunk causing the bark to rot over time.

· Disease, fungi, and insects then have an entry path to spread into the inner layers of the tree.

· Small rodents find protection in the mulch while feeding on the bark.

· Tree roots suffer from lack of oxygen.

· Tree roots can then begin growing laterally, encircling the tree or girdling the trunk, instead of growing out into the soil. The tree’s support system is then weakened which may cause it to topple more readily in a storm.


Eventually, a combination of the above stresses can lead to the decline and death of a tree.


Principles of Tree Mulch There are two important things to remember when applying mulch around your trees.

· The mulch should only be two to four inches deep.

· Keep all mulch at least six inches away from the tree trunk.


The practice of properly spreading mulch to protect tree roots has many benefits.

· Mulch designates a safe distance to keep lawnmowers and string trimmers from damaging roots or bark.

· As organic mulch breaks down, it supplies nutrients to the soil and tree roots.

· Soil temperature is moderated, erosion is decreased, and drainage is improved.

· Weeds are kept at bay, while covering the soil gives a finished landscape effect.


To Rehabilitate Deep Volcano Mulch

· Rake all mulch away from the tree. Break up any clumps. Reapply mulch at a two-to-four-inch depth. This task should be done yearly with properly placed mulch to keep a crust from forming and limiting moisture getting to the roots.

· Make sure that all mulch is at least six inches away from the trunk of the tree.

· Extend the mulch to a new tree’s dripline when possible.


Why are there so many Mulch Volcanoes?

Perhaps the incorrect placement of mulch is caused by the ‘Monkey See, Monkey Do’ principle. Seeing your neighbor or a business applying very deep mulch to trees can seem like the proper method to novice gardeners. Sometimes the incorrect equation: “If a little is good, more must be better!” is followed. (This practice doesn’t work well for fertilizer or weed killer, either.) Residential and business lawn care contractors, as well as homeowners, can be guilty of not taking the time to annually rake out and renew the mulch as needed. Instead, they add more on top of the increasing pile to accomplish that fresh volcano look.


Doing a quick look-up on the internet for mulch will show nothing but trees with mulch right up to their trunks. It is a clean look but not a smart horticultural undertaking. Feel free to use this article to encourage landscape and yard maintenance workers to avoid mulch volcanoes in your yard.


For all your gardening questions, always check with your local County Extension Service. They have information that is scientifically correct for your climate and area of the country. More resources about volcano mulching:

By Sandra Feather


When trees look like telephone poles, they are either planted too deeply or mulched to deeply. Either way, it is not good for the tree. By Sandy Feather


Killed by dogwood borer at work in the mulch volcano. By Sandra Feather

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