How much do you trim back a hydrangea and still get flowers in summer?

How much to cut back your hydrangea depends on the variety of hydrangea you have, and where you live. In northern climates "Annabelle" and "pee gee" hydrangeas can be cut back to eight inches, and still produce a three foot-high shrub with flowers during the summer. "Mophead", "Lacecap" and "oakleaf" hydrangeas set their blooms in late August, September or October, so you have to prune them in early August to be sure you aren't cutting off next year's blooms. Prune out up to a third of the stems of an older plant to encourage new growth. Prune those stems to the ground. Otherwise it usually isn't necessary to prune them at all. Just cut off the spent flowers (deadhead) down to the next stem or mature leaf.