Question
how often and when do you prune hydrangea flower bush.  thanks.

Answer
First you need to find out what kind of hydrangea you have.  Some bloom on old wood, some on this year's growth.  The former should be pruned only to remove excess growth, dead branches etc., because any pruning will be removing some of the flowers.  The latter can be pruned hard first thing in the spring, before growth begins.  In either case once a year is enough.