Yes, this is a photo of a mimosa that is about 55 years old. It first grew slowly into a a shrub/tree about 12' tall with a bit wider spread. Then about 1980, it was badly damaged by locust borers and became a shrub from basal sprouts. From 1999-2009, it was heavily grazed by livestock, had no supplemental water and was more of a herbaceous perennial with a woody rootstock. Since that time no more grazing and I have given it a deep irrigation if the soil is dry in November and again in March and again at bloom time. It gets varying degrees of winter kill (usually about 20-40%). At the time of this photo on August 9 (and today), it is about 7' tall and maybe twice that in spread and loaded with blooms. This is on a farm, fully exposed to the wind, about forty miles out of Lubbock. I think the same thing could be accomplished with pruning.

Thanks for the great testimony! Has it propagated heavily, or is my theory about the cold true in your case?

When I lived on this place before 1988, I had a few seedlings. None survived the winter. Since I moved back in 2007, no seedlings. I have never seen it escape from cultivation or become weedy in this area, though the winters are generally milder now and there is a noticeable heat island effect in Lubbock and more microclimates (buildings and asphalt) in Lubbock. I wouldn't concern myself about weediness.

Good to know. Thanks!