The timing and method of pruning hydrangeas depend on the type of hydrangea you have:
Mophead and Lacecap Hydrangeas (Hydrangea macrophylla): These hydrangeas bloom on old wood, so prune them immediately after flowering, which is typically around late summer. Remove any deador weak stems and cut back the flowered stems to the first healthy pair of buds below the old flower head.
Panicle Hydrangeas (Hydrangea paniculata): Prune these hydrangeas in late winter or early spring, around February or March. Since they bloom on new wood, you can cut the stems back quite hard toencourage vigorous new growth.
Oakleaf Hydrangeas (Hydrangea quercifolia): Prune these hydrangeas after they finish flowering in late summer. Remove any dead or damaged wood and shape the plant as needed.