They will kind of fizzle out in the heat of summer so I would stop dead-heading now. After they stop blooming they look so ugly I pull them. I usually get a fall show from the seeds I toss out or from seeds that fall on their own. They grow so fast, it's easy to start over with them later in the summer for fall blooming.

What Nurmey said. That's what I do.

BTW, while my blue BBs are doing fine re-seeding, I got a minimal re-seed from my black ball. I am going to harvest and re-plant for a second showing.

Strange. Black ball always did well.