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A: There are those who suspect Wildflower Center volunteers are the culpable and capable culprits. Yet, others think staff members play some, albeit small, role. You can torture us with your plant questions, but we will never reveal the Green Guru's secret identity.

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Ask Mr. Smarty Plants is a free service provided by the staff and volunteers at the Lady Bird Johnson Wildflower Center.

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Wednesday - July 13, 2016

From: Boerne, TX
Region: Southwest
Topic: Diseases and Disorders, Trees
Title: Young Mexican White Oak Losing Leaves in Texas
Answered by: Anne Van Nest

QUESTION:

I have a 5 yr old Mexican white oak, 20 ft tall losing its leaves mostly at the top. They turn brown & fall off. It does not lose its leaves in the winter, right?. About 3 ft from the top down is bare, The root flanges are not showing at the base. Could the dirt be piled too high around the trunk? I am letting my hose slowly drip in case it is just too dry. What do you think? Do I have a problem?

ANSWER:

Mexican White Oak (Quercus polymorpha), according to the Texas A&M Forest Service says that this tree is only recently discovered in the U.S. (1992) as a native tree species, but widely available in commercial nurseries. Naturally occurring only in one known U.S. population, near the Devil's River in Val Verde county, but more common in Mexico. Now planted widely as a landscape tree.

The leaves are simple, alternate, 2" to 5" long, highly variable, but often with several shallow lobes or teeth towards the tip. Leaves are thick, leathery, and semi-evergreen, with distinct raised veins on the yellowish underside. New leaves in spring are peach-colored and in colder climates the leaves are late-deciduous and turn yellow-brown.

oak_mexican150.jpg

The Native Plant Database lists this tree as Monterrey Oak as well as Mexican white oak and Netleaf white oak.

Your comment about the root flare is a potential problem. Soil and mulch should not be mounded up around the trunk higher than the root flare.  Howard Garrett, The Dirt Doctor has information and images on his website about Root Flare Management that may be of help to you in determining if your tree is planted too deeply.

 

From the Image Gallery


Mexican white oak
Quercus polymorpha

Mexican white oak
Quercus polymorpha

Mexican white oak
Quercus polymorpha

Mexican white oak
Quercus polymorpha

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