Answer: This is a Hydrangea macrophylla variety and it blooms on wood that grew the year before. Winter damage and/or pruning at the wrong time can limit flowering. If your plants are not sheltered from winter wind and die back to the ground as a result, or if spring frosts nip the flower buds just as they begin to swell, or if you are pruning your plant in fall, winter, or spring, that would explain it. The only time these should be pruned is in summer after they have bloomed. In spring, be very patient before you decide branches are dead and need to be trimmed off-- they may look unpromising but still come back to life as spring progresses.
Hydrangeas also need a certain amount of direct sun, such as in the morning or bright dappled light all day, to bloom. If your plants are in deep shade that might explain it.
I hope this helps your troubleshoot.
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