We bought our black and blue when it was only a foot tall without a single flower. The nursery signage sold us on the plant, but when I got home and read some reviews from other Texans, I was concerned that it might become a garden thug. It spreads by rhizomes. [Shutter] When we moved in, we spent many frustrating months pulling out purple heart, which also spreads by rhizomes, so I had some reservations.
Thankfully we haven't had any trouble with our black and blue. We grow it near a fence so it gets more shade than it would prefer, and maybe that is what is keeping it in check. It's a little leggy but not too much and the looser form means that I'll be able to put some extra plants near its base.