Over-mulched trees

Trees with too much mulch piled on the trunk (right photo) can develop problems at the base of the trunk (click on photo for treatment). It is best to keep mulch 12" away from the base. If you MUST mulch this area apply no more than about one inch on the soil. As a result of too much mulch trunk bark can rot, rodents can burrow resulting in damage to the bark, roots can grow in the mulch and around the trunk, and roots are encouraged to cross over each other. These can cause trees to decline and die. Remove mulch from near the trunk so it remains dry to discourage these potential problems.

The photo below shows a root diving into the soil. This probably resulted from the root growing against the side of the container in the nursery. The mulch becomes a convenient way to hide this potential problem. Although there is no direct research evidence, diving roots appear to make the tree unstable.

Treatment: You have to balance the downsides of leaving this untreated against the downsides of cutting it. Cutting the main root just before it dives is a potential solution but the tree would have to be righted and the cut root buried with a little soil and mulch to encourage new root formation. Click here for more on pruning root defects at or soon after planting.