Creating a “mulch ring” around your trees helps your trees in several ways. Mulch rings create a weed barrier during the growing season. For maximum benefit mulch 2-3 inches deep. The mulch ring protects the tree bark from weed eaters nicking the bark, which over time allows for insects and disease. Mulch also holds in moisture. Remember that trees still need water during the winter months. This also helps protect the tree roots, and as the mulch breaks down it provides nutrients for organic organisms that benefit the tree.