Volcano Mulching

Improper “Volcano” Mulching – Photo Credit: Fredric Miller Joilet Junior College, Bugwood.org

Volcano Mulching is an improper mulching technique where mulch is piled high against the  trunk of a tree.  This is often seen in commercial landscapes; look for it next time you go shopping!   Please don’t do this at home.  Mulch should not touch the trunk of the tree.    The trunk  was simply  not meant to be covered and doing so invites decay and pests; it may kill the tree.

Volcano mulching may cause

  • Disease and decay due to moisture retention on the trunk
  • Insect damage
  • Rodent damage
  • Girdling roots
  • Conditions too damp for the roots or Soil that is too dry since rain may not penetrate the thick mulch layer
  • Failure to develop a normal root flare which stabilizes the tree. These trees may be more likely to fall during a storm.

Proper mulching is very beneficial to trees. Spread mulch 2-4 inches deep to the drip line of the tree if possible; do not let the mulch touch the trunk.  The mulch should form a flat donut with the trunk in the center.   Another guide is the “3x3x3 rule” or 3 inches of mulch, 3 inches from the trunk, in a circle 3 feet wide.  Organic mulches (bark mulch, wood chips, leaves, etc) are preferred over stones or other inorganic products.   Just don’t use too mulch of a good thing!

Benefits of mulch include:

  • Retains moisture.  This is especially beneficial in warm weather.
  • Stops soil from washing away.
  • Organic mulch improves the soil  as it decomposes.
  • Keeps soil temperature more consistent- insulates against cold and heat.
Photo Credit: Joe Murray TreeBio.com, Bugwood.org

The natural mulch is leaf litter. The leaves contain nutrients that the plant has extracted from the soil and so are a perfect soil amendment. Leaves are more likely to stay in place if they have been been mowed or run through some type of shredder.   Some leaves will form a mat (Bradford pear is an example); it is best to compost these before using as mulch.


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