Mexican white oak is drought tolerant, virtually pest and disease free and a fast grower. This trifecta of reasons to grow Quercus polymorpha is often overshadowed by a serious problem.

Most of the trees labeled Mexican white oak on the market are actually hybrids, said Dan Hosage, owner of Madrone Nursery, a native plant grower in San Marcos, Texas.

"Buyer beware, whether you're a wholesaler buying liners or a consumer buying a container tree," Hosage said. "I've seen them hybridized with burr oaks, live oaks, red oaks and chinquapins. And that makes them more susceptible to insects and disease."

But if you ask the right questions and pay attention to your purchase, a true Q. polymorpha is a bonanza for the grower.

Excellent landscape, street tree

Mexican white oak grows up to 40 feet high with up to a 40-foot spread. It has a broad crown and dense branching, complemented by thick, large and lightly serrated leaves. The leaves range from light green to blue green.

It's considered "nearly evergreen." It won't drop leaves until the temperatures hit the teens, Hosage said. New spring foliage emerges pink to red.

It's typically a single-trunk specimen and casts very dense shade at maturity.

In the landscape, this tree is an excellent choice for blocking sound, views or wind. It also makes an excellent city tree, but grackles (nuisance birds) like it, Hosage said. Because the leaves are thick and waxy, don't plant this tree next to a home's gutters, he said.

Besides being a spectacular-looking tree, it has a quirky characteristic. Q. polymorpha puts out two types of acorns that look like they came from two different trees, he said. One is dark brown, narrow and spindly, while the other is brilliant purple and 1-inch across.

"That could be the reason for its species name," he said.

No-frills production

Mexican white oak is shallow rooted and is somewhat indifferent to soil pH, he said. It's basically disease and pest free with no signs of anthracnose, damping off or aphids.

"The one thing I'd avoid is watering them at night. If leaves stay wet at night, fungi will appear and discolor the leaves," he said. "Otherwise it's bulletproof."

It's hardy in USDA Hardiness Zones 7-10, and Hosage said growers outside those areas should try it.

"It's cold tolerant to at least 10 below zero, and it doesn't mind seven months in a row of 90 or 100-plus-degree temperatures," he said. "As far north or east as it goes remains to be seen."

At maturity, it will live on as little as 8-10 inches of rain a year.

Unlike other oak species, this one's easy to propagate.

"It's incredibly easy to propagate from acorns," he said. "Trees will bear acorns almost every year, but it does take a long time to get enough acorns to grow and sell a lot of trees."

But access to clean acorns may cause a bottleneck for future production.

"I haven't tried them from cuttings, but it might work. It's worth a try," he said.

— Kelli Rodda

SPECIFICS:
Name: Quercus polymorpha
Common name: Mexican white oak.
Description: Typically a single-trunk tree with a broad crown and dense branching. Leaves are thick and lightly serrated.
Hardiness: USDA Hardiness Zones 7-10.
Landscape uses: A street tree, shade tree or a barrier against sound, light or unsightly views. Do not plant near a home's gutters because leaves are thick and do not decompose quickly.
For more: Madrone Nursery, 2318 Hilliard Road, San Marcos, TX 78666; (512) 353-3944; http://home.earthlink.net/~madronenursery.

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© 2007 Branch-Smith Publishing