Q. Should I spread mulch under my trees?

A. The benefit of using organic mulch around trees appears to be a guarded secret, because I rarely see it used effectively. There's no other thing you can do for a planted tree that's more beneficial for its health, vigor and longevity than spreading mulch within the drip line of the tree. The drip line is the outer area of the upper canopy that extends farthest from the tree. When it rains, the drip line is the area where most of the water drips off of the upper canopy of the tree. It's also within this area where most of the fine feeder roots reside.

I mentioned "organic" mulch for a reason. Anything that's spread under a plant to improve soil quality, regulate temperature, control weeds or generally contribute in a positive way to the growing environment of a plant can be considered mulch. In some cases it could be rocks, gravel, newspaper or plastic sheets. To get all of the positive effects out of mulching a tree, I always prefer the application of organic mulch, such as wood chips.

We're trying to duplicate the conditions that are found in a natural environment, such as in a forest of naturally germinated trees. The trees took root from a fallen seed or acorn and landed in exactly the right spot and germinated under natural conditions. If the seed then finds enough water to sustain itself through hot summers and isn't eaten by squirrels or deer, it can thrive on its own.

You'll notice that the tree is growing in a thick layer of fallen leaves or needles that have accumulated over the years, effectively covering the entire root system of the tree. As the leaves or needles accumulate, this natural mulch regulates the soil temperature and holds moisture in the soil for many months beyond the last rainfall. It also creates a perfect medium in which new seedling trees can germinate.

Yes, you should mulch your trees. Use organic mulch, like wood chips, and spread it at least three inches thick within the entire drip line. Just be careful not to pile it up against the base of the tree.

David D. Mortimer is a certified arborist with more than 30 years experience in the tree care industry. E-mail questions to dmortimer@theacorn.com.

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