The lawn mower was supposed to circle the newly planted sapling, but instead it struck the base. Oops! Is that a problem?
Yes, it is.
Unlike skin, wounds that reach below the bark don't heal. At best, the trunk seals off the injury, but there is no repair in the sense that our skin repairs itself. Bark will form a callus along the edge of the wound, but it rarely can bridge the break. The trunk typically loses the bark in the injured area, and the wound remains decades later.
University of Illinois Extension horticulture educator Nancy Pollard recommends protecting against lawn-mower bites by mulching.
"When planting a new tree, take the time to remove grass at least two feet away from the base. Put down wood-chip mulch to a depth of about three inches.
"Mulch should ring the tree like a lifesaver, not a volcano. A ring of mulch protects the tree from injury, keeps roots comfortably cool, reduces water loss, and keeps weeds at bay."
The best technique is to mulch just to the bottom of the root flare, without piling it up the base.
If the tree isn't planted too deeply, you will see a slight flare where the roots naturally form. Trunk tissue at and above the flare is usually water resistant, not waterproof.
If it is not allowed to dry out, eventually insects and diseases attack wet bark.
"People enthusiastically pile mulch at the base of the tree, not knowing it will soak and injure rather than protect it," Pollard warns.