Ask the Gardener: Why Is Mulch Used Around the Base of a Tree?

Ask the gardener is a column in which local readers send in questions about your garden, lawn, trees and more.

Reader question: "For most of the last 35 years, I have been in Texas. We have always learned that when you plant a tree, it goes below the level of the ground a bit, and you do NOT build the earth up around the trunk. Here in Wentzville, it seems that every new tree I see has the mulch built up in a mount around the tree base.  Isn't that bad for the tree?

Expert Answer: According to TreesAreGood.com, there's a method to the mulch madness. 

For one, it can be a cosmetic improvement. Mulch at the base of the tree shows care and effort has been put into the lawn. Aside from looking nice, mulch is supposed to help control weeds. TreesAreGood says a two- to four-inch layer of mulch makes it harder for weeds to grow. Without weeds, the tree is also protected from weed whackers and other lawn-maintenance tools. 

Mulch is also good for providing soil moisture for the tree, meaning you it will need less watering to grow bigger. Mulch also is good for keeping the soil warm in the winter and cooler in the summer. 

Basically mulch is intended to act like leaves and other helpful debris found at the base of trees in the wild. 

It's important to note, however, that there can be too much of a good thing. So-called "mulch volcanoes" can kill trees instead of helping. The volcanoes can cause roots to spread up and can cause fungus problems for the trees