Picture for reference.

Deadheading hdrangeas does not encourage reblooming. A growth point (the terminal ends of stems) once finished flowering for the season will not produce new flower buds that season. The plant could produce new flowers later in the season elsewhere on the plant (dependng on type) but that would be independent or unrelated to any deadheading.

But you can deadhead to remove old flowers any time you like. Many like the appearance of the aging flowers and just leave them in place until they disappear on their own or are removed in late winter/early spring. It is your choice.

Thank you gardengal48. I may deadhead some of the blooms and leave others. Learning as I go!

I do not deadhead 'Incrediball', the aging blooms remain attractive as they turn green and stay looking good for a long time, just be sure to keep the plants well watered! Late last summer, I had cut and dried many in water (yes, in water) and they turned out very well.