Ask Mr. Smarty Plants

Quercus polymorpha (Mexican white oak) - also known as Monterrey Oak - is only native to Val Verde County in the Big Bend area of West Texas, as you can see from this USDA Plant Profile Map. That doesn't mean it won't grow in Central Texas,  of course,  it will, but it does mean this is not exactly the best place for it. We are wondering who recommended that you use it as a heavily pruned tree for a privacy hedge? If it was a plant seller, we would think they could give you instructions and results on the procedure. 

From our webpage on that plant;

"Conditions Comments: This species is widespread in Mexico and found in a few west Texas canyons. It is a relatively fast growing oak, and practically evergreen in Austin. It is more resistant to oak wilt and other diseases and pests than other oaks."

While it notes that this oak is relatively fast-growing, it will be on its way to growing to a mature height of 36 to 72 feet tall. That's a WHOLE lot of pruning! Even though is is somewhat resistant to Oak Wilt, Austin is something of an Oak Wilt center, and we would not be comfortable if we did not recommend putting pruning paint on any cut made on the branches of this tree, which is a whole lot of pruning paint.

From Dave's Garden:

"There is a beautiful specimen of this tree near my home in south Austin (Texas). It is about 45 feet tall and very healthy. That particular tree is about 17 years old I am told. Based on this, I planted two in my yard in January, 2007. 13 months later they are doing just fine. I would not, however, call it evergreen, at least in central Texas. The tree starts losing foliage in December and January and can be mostly bare by late February, but quickly starts putting on new growth shortly there after. By early March news leaves are budding out in profusion."

So far, we have not seen a single reference to pruning it to a bush. We will try another search on the Internet on "pruning oaks into bush shape.":

From Texas A&M Earth-Kind Follow Proper Pruning Technques

Mostly, our search produced advice on pruning shrubs into shrubs, not trees into shrubs. Since we have about exhausted our resources trying to find the directions you want (which may be because they don't exist) we are going to suggest some evergreen shrubs that might work in the same situation.

We went to our Native Plant Database, scrolled down to the Combination Search, and searched on Texas, "shrub" for Habit, "evergreen" for Leaf Retention, "dry" for Soil Moisture and 6 to 12 ft. for Height. Here are our four results:

Quercus turbinella (Sonoran scrub oak)- grows 6 to 12 ft., is also native to Val Verde and other counties in far west Texas, not in Travis County. Pictures

Garrya ovata ssp. lindheimeri (Lindheimer's silktassel) USDA Plant Profile shows it growing naturally in Travis County.6-12 ft.

Mahonia haematocarpa (Red barberry), 6-12 ft. USDA Plant Profile shows it growing pretty much in the same areas as the Sonoran Scrub Oak, again not in Travis County.

Rhus virens (Evergreen sumac) 6-12 ft. USDA Plant Peofile shows it growing in Travis County as well as some of the far western Texas counties.

Bottom line: We don't think attempting to trim a potentially 72 ft. tree into a shrub is a very good idea, but you did ask.