A: No, it isn’t! You can plant the vast majority of trees and shrubs all winter long in North Texas, as long as you know where those shrubs have been held at the nursery. Plants require a certain amount of hardening-off to tolerate the winter – that’s time exposed to cooler temperatures and shorter day lengths. With greenhouses, plants don’t necessarily go through that process! Additionally, freshly arrived plants from a much warmer climate (south Texas, Florida, and the like) sometimes need a bit of time to adjust.
As long as the plants you purchase haven’t been held for weeks in a sealed-up or heated greenhouse or aren’t fresh off the truck from a much warmer climate, almost any common tree or shrub that will tolerate our normal winter planted outside in our area is fine. And those plants will be fine with a few weeks of exposure to cooler weather to toughen up. Water your new plantings well the day before a forecast hard freeze.
If your plants are hardened off properly, and of a species that will normally tolerate our winter, go right ahead and plant.