Experts and BHG readers answer.
non blooming big daddy hydrangea
You might have to be patient, depending on how severely you pruned them, and wait until next growing season. In addition, your zone is one zone colder than the recommended zone for this plant. If the shrub is in a protected area, that might not matter. I would also have the soil tested by your county extension service to be sure it is not too alkaline for this plant.