Bat Face Plant

I bought this Bat Face Cuphea (Cuphea llavea) in July, from Orchard Nursery in Lafayette, CA and planted it in a half wine barrel along with some other plants. The tag says it will grow to 18" tall, but really it just trails over the side of the barrel in a beautiful cascade of red and purple flowers. I've seen quite a few hummingbirds hanging out by this plant. It supposedly does great in the heat, and is also drought tolerant, but it requires excellent drainage. This perennial is also supposedly frost hardy in the upper 20's and root hardy in the lower 20's. I'll be leaving this out all winter in the wine barrel that has a southern exposure to see if it's true...