Article 5 of 12 from Trees: Dispelling Myths & Misinformation, prepared by the arborists of the Southwest Division of Bartlett Tree Experts as a community education initiative.
You see them everywhere – those volcano-shaped piles of mulch built up around the bases of young trees. It must be correct practice because often these mulch volcanoes are applied by “professional” maintenance companies. That sounds logical, but it’s wrong.
The previous article described the importance of planting a tree at the right height so the root crown develops above grade. After all of that effort, why undo it by building up mulch around the trunk! This practice creates a moist, dark environment that attracts insects and diseases. It draws rodents that gnaw on the “protected” bark, which can interrupt delivery of moisture and nutrients to the tree. It lures newly developing roots away from the soil and into the mulch mound. These roots often circle the tree, and we’ve already learned what girdling roots can do.
The mulch applied to a newly planted tree should be no more than two to four inches deep, away from the trunk, and spread out to the drip line. Wood-chip or other organic mulch applied in this manner will help moderate temperatures, retain moisture, improve soil quality, and discourage lawnmower and weed-whacker damage of the trunk and surface roots.
Keep your eyes open for mulch volcanoes in neighborhoods, public places, and at businesses. Better yet, make a game of it for the kids. They’ll spot them everywhere (unfortunately), but it might motivate them to become more avid students of responsible tree care.