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Gardening tips on mesquite roots rising to the surface

Author: Cathy Cromell
Issue: July, 2013, Page 123


Q - According to the landscapers I use, large roots from my mesquite tree are rising to the surface of the soil in search of oxygen and water. They are recommending an expensive treatment that involves deep-pressure watering and feeding. Do you have any advice?

A - If your trees are located in a lawn, that’s the most common reason for roots to grow close to the surface of the soil, because that is where the water is, explains Certified Arborist Cathy Rymer, water conservation coordinator for the city of Chandler, Arizona. Lawns are generally watered only to a depth of about 6 inches, so there is no reason for roots to grow deeper. Over time, roots increase in diameter and can sometimes be seen on the soil surface.

Surface roots also can be caused by a layer of plastic installed under gravel mulch as a weed barrier, a practice that is no longer recommended because water condenses and accumulates under the plastic and on top of the soil. Plastic can restrict the amount of oxygen available, as well.

Assuming you don’t have plastic, there should be plenty of oxygen in the top 18 inches of soil. Normally, this is where 90 percent of tree roots are located, with the feeder roots, just under the surface. A few anchoring roots go deeper to support the tree. If water soaks down into the soil from rain and your irrigation system, oxygen also will penetrate into the soil. As the water soaks in, it will carry down any fertilizer you apply.

Where you apply water is extremely important. Established trees do not have feeder roots next to their trunks. Most of the roots that absorb nutrients and water are located at the drip line, or at the edge of the branches, so this is where water should be applied.

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