"Volcanoes" are a leading cause of ornamental tree injury and death

Well, we're not exactly talking about a Pompeii situation, but mulch volcanoes are a major threat to our trees and shrubs! Read on to find out how you can make a difference.

What is a mulch volcano?

A very sad tree trapped in a mulch volcano (photo from Greg Jordan, UNH Extension).

We've all seen it- a well-meaning gardener wants to protect their trees and piles tons of mulch around the trunk to reduce weeds, regulate soil temperatures, and increase moisture retention. The problem is that tree trunks need to breathe! They're not designed to be underground.

When mulch is in contact with the trunk for extended periods of time, it holds in too much moisture, leading to bark infections and decreases the ability to transport oxygen and nutrients. The tree will be confused and will likely try to send out roots from the trunk, which can end up girdling the plant. As the mulch decomposes, it also puts off heat, which can damage the bark.

Additionally, if there's too much mulch piled up on top of the roots, it prevents the roots from getting oxygen (yes, the roots also need to breathe!). Finally, if the mulch dries out completely, it can actually become hydrophobic and prevent water from infiltrating into the soil, which will also make your tree sad!

Proper mulching for trees

This tree was buried far too deep! We had to excavate the trunk down several inches.

When mulching your trees, make sure to first remove old mulch from directly around the trunk. You should be able to see the root flare: if not, keep digging! If a tree was planted poorly, it could be down pretty far.

Once you can see the root flare, place 2-3" of mulch out to the drip line. Place only a light coating around the trunk. Your mulch should be a doughnut shape, with the thinnest layers around the trunk and outer edge!

A better option than mulch

If you want to upgrade your tree rings, consider planting some native plants as a "living mulch"!