I can remember a time when people didn't use mulch. When I first started my career in the nineties, County Agents like me had started encouraging people to use mulch. Mulch protects the roots of plants from cold or heat damage, retains moisture, prevents soil compaction and eventually breaks down into beneficial organic matter.

Mulch is great when used properly. However, it can be detrimental to plant health when used in excess. Mulch should only be 2-3 inches deep around plants over the root zone. When mulch is deeper it actually can smother roots depriving them of oxygen.

When mulch is too deep, roots will need to get close to the surface to get oxygen. These roots will circle around in the mulch causing girdling roots. Girdling roots will eventually grow into the stem and strangle the tree.

Hardwood mulches last for years. We do not need to add new mulch every year. If you do want to keep your mulch fresh by adding new each year, it is recommended that you remove the old mulch. If you do add mulch every year without removing the old mulch, then eventually you end up with a deep pile around the plant. Shallow mulch will decompose slowly; deep mulch will begin to decompose, become a compost pile generating heat and damaging roots and the trunk.

Excessive mulch can damage the trunks of plants. The bark that is on the roots of a tree is resistant to rot. The bark on the aerial portions of the tree such as the trunk is not rot resistant. Mulch will hold moisture against the bark of the trunk and eventually it will rot exposing the inner wood of the tree to decay fungi and bacteria. Over time, this rot can lead to the tree failing.

A good way to avoid over-mulching and at the same time recycle your leaves in the fall is to use them as mulch. Do not worry about piling leaves up around trees. Leaves decompose quickly. By the end of the winter, twelve or more inches of leaves will be flattened to the ground by rain and snow.