Mulch Mounds! Oh My!

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WATCH OUT FOR MULCH MOUNDS

By José Fernández

Two days ago I stopped by the local gas station/grocery store compound around sunrise to replenish my truck’s fuel tank. As I drove on the service road passing the commercial property I felt something strange tugging at my peripheral vision, like large chocolate chips dotting the edge of my field of view. I took my eyes off the road for a moment, and sure enough, seemingly overnight the landscape had changed. It was as if a very large community of rodents had decided to move in and dig burrows in the landscape, leaving all the soil in regular mounds, perfectly spaced on the lawn. The next moment I saw that each mound had a tree growing out of it.  Then the colors of breaking dawn also brought the light of knowledge to me as I realized “It’s spring, and the mulch mounders are at it again”.

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You know when these mysterious beings have been in your neighborhood because all of a sudden trees look like they decided to burst fully formed out of the soil, shouldering through the earth’s crust, leaving it mounded up at the base of their trunk.  You know you have been visited by a very dedicated contingent of mounders when even telephone poles or street signs are enjoying the benefits of multiplying mulch.  (Yes, though this sight was unrecorded, I have heard eyewitnesses testify to it).

Please forgive my attempts at humor.  It really is light-hearted, and I bear no ill will to the people who deliver the mulch so generously.  As an arborist, I do take issue with the practice itself though, for three main reasons that perhaps are not immediately evident to those trying to do a good deed:

The mulch mound around the base of this tree has caused new roots to grow around the root flare. These new roots are now girdling (choking) the tree causing it to decline (see lack of leaves/growth in the crown of the tree).

  1. Mulch can create a hardened hydrophobic layer that actually sheds water.  This effect is made worse when the mulch is mounded in a way that directs water away from the root crown of a tree, where all the roots are on a newly planted tree. 

  2. When the root crown is buried in such thick mulch, new roots start forming, trying to grow up to a more favorable place (the surface), where water and oxygen are more readily available.  While they grow, they will likely stay contained within the mulch ring, which can contribute to a circular pattern of growth, causing girdling of the stem in later years. (See photo).

  3. When enough water is provided to saturate the mulch, moisture will persist for longer periods of time around the trunk tissue.  This, combined with warm temperatures from the composting process, provides a favorable environment for pathogens like bacteria and fungi to develop and cause disease. 

Bad vs. Good mulching techniques // Proper mulching around a tree keeps the root flare visible while having about 2 inches of mulch depth on the root zone.

Why do we mulch anyway?  For very good reasons.  Established mulch rings help keep weeds away, help maintain moisture levels, provide organic matter for the soil (improving both chemistry and structure), and maintain a clear zone where mowers will not enter and cause soil compaction or mechanical damage to the tree.  Like anything else in life, any good thing carried to an extreme usually ceases being a good thing.  Overmulching actually defeats some of the reasons for mulching to begin with!

There you have it.  Even the topic of mulch leads to a basic principle in life: Too much of a good thing… can lead away from what is good.

Here’s another one: Mulch mounders are people too, and I can live alongside them in peace as fellow human beings.  But the practice of mounding mulch makes life difficult for trees.  They can’t run away, they can’t open up their mouth and bawl for help.  So I have to speak up for them if I can.

And I can.

Thank you for reading!  I appreciate your comments and your thoughts.

Your friendly neighborhood arborist,

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José Fernández | Regional Manager, Russell Tree Experts

José became an ISA Certified Arborist® in 2004, and a Board-Certified Master Arborist® in 2015. Currently he is enrolled at The Ohio State University pursuing a Master’s Degree in Plant Health Management. José likes working around trees because he is still filled with wonder every time he walks in the woods. José has worked at Russell Tree Experts since 2012.