This is Hydrangea Serrata Preziosa. It's the second year that I've had it and it's had a wonderful season so far. While it's similar to a mophead hydrangea, the flower clusters are slightly smaller. What I like most about it is the way it changes color. When it first bloomed in late May, it was a very light pink, and now it is a deeper burgundy.
I have this hydrangea planted alone in a terra cotta pot that's about 19 inches in diameter. During these sweltering few days that we've had, I've had to completely soak it every day. It likes full to part sun, is hardy to zone 5, and grows to about 4 feet. Also, it blooms on old wood so be careful about pruning--only cut spent flowers or damaged stems.
This is the third hydrangea in my container garden collection. It joins my Endless Summer and Pee Wee Oakleaf.