Volcano of mulch – Don’t let this problem erupt in your yard!

Q. I hear people talk about not making a volcano of mulch around the tree. What is it and why is it bad?

Great question that we get asked a lot! You will never see hot lava erupting from the top of your trees so no worries about that!

The danger of volcanoes of mulch around the trees is what you don’t see…

Volcano Mulch Ring

“It looks pretty!  Why is it bad?”  Just like your skin the bark of the tree is meant to breathe.  If you wore wet socks for a year – what would your feet look like?

The constant moisture, lack of light and airflow cause ROT.  Rot is bad!  Especially at the bottom of the tree.

Volcano Ring Damage

Mulch is supposed to achieve these main goals:

  • Retain soil moisture just not excessively
  • Suppress weeds
  • Moderate soil temperatures

The excessive piled mulch softens the bark of trees 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.  Mulch rings should be wide, not tall and deep.

Another issue besides rot is 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.

Basic Mulch Tips:

  • A one to two-inch layer of mulch helps suppress weeds and retain soil moisture. As it breaks down, it provides organic matter to the soil.
  • Organic mulch comes in many forms, including shredded hardwood bark, pine bark, pine needles, shredded cedar and cypress, wood chips and colored bark. Make your own mulch with shredded and semi-decayed leaves, known as leaf mold, or from rotted and screened compost.
  • Mulch can be ordered and delivered in bulk, which will reduce the cost of mulching large areas. Mulch merchants sell it by the cubic yard and may require a minimum amount for a delivery. A cubic yard of mulch, laid to a depth of two inches, will cover about 160 square feet.
  • Bagged mulch is more expensive but far easier to carry and spread than a huge pile of bulk mulch.
  • Mulch that smells of vinegar or worse has been improperly stored and contains harmful acids.
  • Mulch that smells of a rich molasses aroma has a healthy aerobic activity.

Concerned about your tree?  Have our ISA Certified Arborist evaluate your tree.

978-706-1038

3 Comments
  1. I did not know there was so many types and forms of organic mulch out there. I’m trying to landscape my backyard, and am looking to mulch my garden before I plant anything. I’ll be sure to get bagged mulch, because as you say it is easier to carry and to spread in the yard. Thanks for all the helpful tips.

  2. You got a very wonderful website, Gladiolus I noticed it through yahoo.

  3. Thanks for the writeup on the dangers of mulch volcanoes. It’s definitely a no-no, and yet I see it all too often around my neighborhood. You need to keep it shallow around the base.

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