If kept deadheaded, they will bloom all summer and into early fall in my area. Sometimes they even reseed themselves.

I have a couple that're 5-6 years old in a bonsai pots & can't keep them from blooming unless I cut the bloom buds off. If I get lazy & forget or ignore them, they really suffers as a result of having to devote all that energy into making blooms. As SH said - dead-heading is key in keeping it in reproductive phase.

Al

I'll vouch for those answers. I used to think of them as only cool weather plants, but I have a golf course who buys me out of them every year. I asked the groundskeeper why so many? and he said the same thing. Regardless of the heat, if he keeps them deadheaded, they crank all summer reliably.