Why do hydrangeas have varying numbers of blooms from year to year?

Do you prune them at different times in different years?

No I leave the dead blooms on to protect the new buds from frost.

Do you think that during the drought earlier in the year they had enough water, or even last year, they really need a lot. Mine this year had a lot of dead wood and its much shorter than it was last year,although its flowering well, its not been an easy time for anything in the garden.

As with Pamg I've found a lot of dead wood on hydrangeas and the flowers, even this year have been smaller. I've said before that some of the things we are seeing now is as a result of the bad winter. No flowers still suggests either frost damage or pruning. When you take the old flowers off how far do you cut back?

Thank you everyone for your replies. I'm thinking it may be a combination of poor pruning and lack of water. One of my hydrangeas is in a pot and it could have dried out at times last summer.

Water is crucial mines in the ground and even after all the rain( we're on clay) a couple of hot days and it began to wilt