Mulch wide, not deep! Volcano mulching is a common yet harmful practice that leads to poor drainage, root rot and, at the very least, poor root growth. Deep mulching, as shown in Figure A below, stresses the tree’s stem tissues and may lead to insect and disease problems. We recommend applying a thin layer of mulch around trees and maintaining a safe distance of 4 to 6 inches from the base of the tree as shown in Figure B.