Apply fresh pine bark mulch only after the old layer has decomposed. Don't pile it up against the trunk.
So much fuss has been made about the benefits of mulch that it’s not surprising that some people overdo it. They think if a little around trees and shrubs is good, a lot will be even better. Without checking first to see whether the previous mulch has decomposed, they automatically add a fresh layer each year. Over time, this accumulated mulch can injure or kill the very plants it was put there to help.
How can you tell if your tree or shrub suffers from over-mulching? Signs include abnormally small leaves, chlorotic (yellow or blanched) foliage, dieback of branches, dying grass outside the mulch around the plant, and basal cankers on the trunk where it touches the mulch.
- Don’t apply fresh wood mulch over mulch that’s already there. Allow the existing layer to decompose first. Apply a maximum of 2 inches at a time.
- Don’t pile up mulch against the trunks of trees and shrubs. This can cause cankers on spruce species and encourage borers on hardwoods.
- Don’t worry about over-mulching with pine straw. This material rots quickly and seldom builds up to damaging levels. However, don’t apply more than 2 to 3 inches at a time.