(Editor's note: This column ran in 2017 and Eddie Wheeler has long since retired from the Marshall County Extension office. But alert reader Eddie Allen asked that we re-post this story. He said the "volcano mulching" referred to here is a common sin he sees as people spruce up their places for spring.)
A few weeks ago, I wrote an article on fall as a good time to plant trees. An important phase for newly planted trees is mulching.
Mulching trees provides several benefits to the tree, provided it is done properly. Mulch comes into play when a new tree is planted to keep its root system covered and improve its look aesthetically.
Mulching does a variety of things. It helps hold nutrients in the soil so they are not lost to the atmosphere (particularly important for young and new trees). It prevents weeds from emerging or at least hinders them. It holds moisture in the soil. It prevents compaction to the soil, which is bad for root development.
It is aesthetically pleasing, and it reduces the amount of freezing and cold exposure to the root system by insulating the ground.
One issue that is often seen is a "mulch volcano." A mulch volcano is a large buildup of mulch, placed up the tree trunk. This is unhealthy for the tree’s length of life and will eventually kill it.
When a thick layer of mulch is spread around the trunk of a tree, many things can happen, and they’re not good. The mulch will indeed hold moisture, but it will be up against the tree trunk, creating a condition where the bark starts to decay. This problem allows fungi, bacteria and insects to get under the bark and cause problems for the tree.
Furthermore, a mulch volcano provides an opportunity for the tree’s roots to grow around the trunk. As the roots elongate over the years inside of the mulch volcano, they encircle the trunk. This is called girdling. The girdling action literally strangles the tree and deprives the roots and canopy of necessary resources.
As the tree declines in health, it becomes more susceptible to attack from pests, diseases, and harmful fungi. Circling roots are another problem commonly found in mulch volcanoes. In this moist environment, a tree will begin to grow roots into the mulch instead of outward into the surrounding soil.
Most mulch volcanoes are circular because that’s the way it is placed around the trees. Roots will start to circle the tree, staying in the mulch. However, the tree does not die immediately. It goes through a prolonged period of decline.
Proper mulching provides outstanding health benefits to trees and shrubs, such as helping retain soil moisture, regulating soil temperatures, and improving soil conditions. The proper way to mulch a tree is to first spread an even 2- to 4-inch layer around the base of the tree. Extend the mulch to the outer edge of the tree’s canopy if possible. Make sure there is no mulch within 3 to 6 inches of the base of the tree. Prevent one of the worst problems by mulching properly and avoid the mulch volcano.