Mulch 'volcanoes' around trees look good but have negative effect on plant

Volcanoes are a wonder of nature. You can be amazed watching lava as it flows down the side of a volcano. Some might say that there is beauty in the lava flow. Volcanoes are very destructive, however, and we take notice when one becomes active anywhere in the world.

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Lately, I have noticed that there are small volcanoes popping up in our area in greater and greater numbers. I am not talking about the kind of volcanoes that produce lava and spew ash into the air, but the kind that have trees growing out of them. Maybe you have noticed them, too.

These volcanoes are made of mulch. The mulch around the trees is a few feet in diameter, but extends up the trunk of the tree. I saw a tree the other day where the mulch extended about two feet up the trunk of the tree. These volcanoes around trees can be detrimental to the health of the tree.

There are several problems that can occur when mulch is piled around the trunk of trees. The first is that you have an increased chance of disease and insect problems. The mulch increases the moisture level around the trunk of the tree. This allows fungus organisms that cause rot to infect the tree. Also, the mulch gives insects a place to live as well as hides the damage caused by these insects. Fire ants like these volcanoes, which can make it difficult for us to work around these trees.

Another problem is these volcanoes can harbor other unwanted guest such as voles. Voles are rodents that live under deep mulches or use mole tunnels. When mulch gets too deep, it makes the best habitat for voles. They eat plants, especially the root system. Most people don't know that they have a vole problem until plants start dying. When you pull back the mulch, you will find plants that are girdled or you can pull up the plant because the root system has been eaten.

There is another problem that occurs when you put too much mulch around plants. The root systems of the trees tend to send its root system into the mulch. The reasons for this is that too thick of a mulch layer can reduce the amount of oxygen and water getting to the root system. The root system will grow into the mulch because of the better growing conditions. However, when the mulch dries out from lack of water, the root system will die. Another tendency of plants that have too much mulch around them is to produce a second root system. This root system is above ground and grows into the mulch. When a second root system is produced, the first root system usually dies.

So, why are mulches important and what is the right way to mulch trees? Mulches are important because they aid in the establishment and growth of young trees. They conserve moisture by reducing evaporation from the soil surface. They help reduce soil erosion and water run-off. In our clay soils, mulches help with soil compaction and help with competition from weeds. Mulches can reduce the summer soil temperature which creates a better environment for the roots.

The proper way to mulch around trees begins when you first plant the tree. The mulch needs to be three to four inches deep. You need to start the mulch four to six inches away from the trunk of the tree. This allows the trunk to stay dry to reduce the disease and insect problems. The mulch needs to extend to the edge of the canopy or further. As the tree gets larger, increase the size of the mulched area.

Now, the question is what needs to be done with the tree that has a volcano around it. You need to slowly pull the mulch away from the tree trunk and spread it out around the tree. If you start uncovering roots, you need to stop and leave a layer of mulch on the roots. If you don't hit any roots, keep pulling the mulch back until you have four to six inches of air space around the trunk and a mulch depth of three to four inches.

Volcanoes around trees, like the real volcanoes, might look good from a distance, but they are detrimental to those who live close to them. So, we need to use mulch in the proper way to help keep our trees and plants healthy.

Columbia County Extension Agent Charles Phillips can be reached at (706) 868-3413 or by e-mail at charlesp@uga.edu. The Extension Web address is www.ugaextension.com/columbia.