This latest mulching technique that is detrimental to trees has been nicknamed “Volcano Mulching” for good reason. I’m not sure where or how this started but it is destroying trees in landscapes across America. Probably beyond our borders as well, but I don’t know for sure about that.
Take a look at these two photos.
Notice how high the mulch is around the trunk of this tree. That is not good. All plants, trees and shrubs, have a root crown. That’s the point where the roots stop and the upper part of the plant begins. Roots need to be covered with soil at all times and not exposed to air. Roots know how to deal with moisture and are designed to absorb moisture to provide nutrition to the plant. The stem of trees and shrubs should not be subjected to the same kind of moisture. It will damage the stem of the plant.
The two photos that I am showing you here have way too much mulch around the stem of the trees. In other words, the mulch is too deep. Actually these two trees are mildly over mulched compared to many that I’ve seen. When you pile the mulch up around the stem of the tree the excessive moisture that the mulch traps will begin to decay the bark of the tree. Pretty soon the bark will begin to pull away from the tree, exposing the cambium layer to the air, and allowing insects, disease and fungi to go to work between the bark of the tree and the tree itself. Eventually the tree can die.
It’s important to understand that right below the outer layer of bark is a layer of tissue known as the cambium layer. The cambium layer is the circulatory system of the tree. All of the moisture and nutrition that feed the tree travel through that cambium layer. That’s why it is so important to protect the cambium layer.
When you plant a tree or shrub you should never plant it so anything except the root crown is covered with soil. In most cases I suggest people install plants so the root crown is at least one inch above grade, then covered with soil and a light layer of mulch. No more than two to three inches of mulch and even that should be pulled away from the trunk of the tree so there is air flow between the mulch and the trunk of the tree.
Where and how this volcano mulching thing started I have no idea. I first started working in the landscape trade when I was 18 years old, that was almost 40 years ago, and we never did this volcano mulching thing, nor did anybody else. But then a few years ago I started seeing these huge piles of mulch around the base of trees in parking lots etc. Then unknowing homeowners see this practice and start repeating it at home.
You’d think that people in the industry, meaning the landscape contractors that take care of these commercial properties, would know better. I’m sure most of them do, but it’s the few that seemed to have started a trend that truly needs to be reversed. Believe me, I’m not the only one on this band wagon.
Be kind to your trees.