How do you trim flowers off a hydrangea bush?

They never need to be pruned. Now if you wish to remove the dead blooms that is fine. You do this with small shears or garden sissors just below the bloom. Now if you feel that the bush is just to big for you, you will need to wait until after the spring. They produce their blooms for the next year in the fall so if you trim them then, you will loose your next years flower. So wait until after the spring bloom and before Aug. to do this.