I'm not too sure what you mean by florist's Verbena. There are several Verbena's that are native and/or suitable for Xeriscaping. Also, many old-fashioned turn-of-the-century plants turn out to be good for Xeriscaping, even if they aren't described as "Xeriscape" plants (probably because they had to hand-water the flower garden back then!) If you have a cheap/free source, give it a try. If you have to buy it - get it from a source that either has complete info including water requirements on the plant tag, or has knowledgable staff to help you.
I was not sure what florist verbena meant, either. It means annual verbena, I surmise from looking on-line. I also have a wildflower verbena which self sows and blooms every year. Thanks, pollengarden. Luciee