Answer: The answer to your question depends on what kind of hydrangea you have. The big leafed hydrangea (H. macrophylla) and the oakleaf hydrangea both bloom on old growth from the year before, so the time to prune these is in summer right after it blooms. Prune at that time for shape or with an overgrown plant, thin out some of the oldest branches. Also, in late spring, if necessary, trim off winter-killed tips but keep spring time pruning to a minimum as it will reduce blooms that summer.
H. arborescens should be trimmed off very short in late fall or early spring. It regrows and blooms on the new growth.
H. paniculata (PeeGee hydrangea) is a woody shrub and can left with minimal pruning, or it can be shaped as desired or even trained as a tree form. This one blooms on new growth of the season so any pruning is best done in late winter to early spring. Broken or damaged branches should be neatly trimmed off as soon as they occur.
You may cut any hydrangea's blooms for fresh bouquets and/or deadhead (remove faded blooms) as soon as they fade or any time after that, as you prefer.
I hope this answers your question.
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