Mulch Volcanoes No Friend To Trees

 Written By Tom Valovic
 
You’ve probably never heard of mulch volcanoes. Neither had I until recently. But one of the nice things about volunteering for an organization like the Worcester Tree Initiative is learning more about how to foster healthy growth of green spaces in urban areas.  Creating and nurturing the trees that are foundational to those green spaces may seem simple but doing it right has its own complexities. As a former research analyst, I dug into this issue a little (so to speak). Here’s what I found.
 
Placing mulch volcanoes – also known as cones ---around the base of a planted tree is a widespread practice. But the problem is that it’s tantamount to over-mulching the tree; in other words, too much of a good thing. These mulch mounds can be as high as a foot or a foot and a half above the base of a trunk. It seems to be a safe bet that landscapers and other professional growers would know what a poor practice this is. But WTI is working to get the word out that this simply isn’t the case.
 
Why is this such a bad practice?  Simply put, this kind of over-mulching is bad for a tree’s health and can even eventually kill them. Here’s what an article in the  “Washington Post” said about this topic:
 
“Mulch is supposed to achieve these main goals: retain soil moisture, suppress weeds and moderate soil temperatures. The root zone of an established tree extends beyond its drip line, so mounding the mulch against the trunk does little for the roots, except to cause the roots immediately around the trunk, especially in young trees, to grow into the volcano. Also, the piled mulch softens the bark of young trees and trees with smooth bark, such as maples, beeches and crape myrtles, and invites insects, rodents and diseases to invade. The lower trunk, unlike the roots, cannot survive long-term with the constant moisture trapped by the collar of mulch. It is the equivalent of planting a tree too deeply.
 
The roots of a tree or shrub find their own level in an attempt to balance their needs for water and air. If you pile mulch too thickly above the roots, the existing surface roots are suffocated and new ones grow into the mulch. Not only does that leave them at risk of drying and dying when the mulch decays, but the roots "grow across the stem, potentially strangling the tree to death”… research scientist Jeff Gillman writes in his new book, "How Trees Die" (Westholme, 2009).”
 
In addition, the widespread use of mulch volcanoes sets a bad precedent. Homeowners see this happening extensively and assume that landscapers are engaged in a best practice. To compound the problem, those landscapers that are aware the practice is harmful apparently aren’t always educating those customers who ask for the volcanoes.
 
Like anything else, the cure for this practice is education and greater awareness. According to Ruth Seward, WTI’s executive director, WTI will be developing several educational initiatives in 2018 to address this issue. Stay tuned.  
 
– Tom
 
Tom Valovic is a volunteer with the Worcester Tree Initiative and a freelance writer and editor. Tom has written articles for “The Boston Globe”, “Annals of Earth”, “The Whole Earth Review”, and other publications.