Hydrangeas that bloom on old wood are the earliest to flower in spring. Those that bloom on new wood during the current year bloom in summer. Some such as Endless Summer bloom on both and are repeat bloomers.
Some Hydrangeas that bloom on old wood:
Hydrangea quercifolia – Oak Leaf – Alice, Ruby Slippers, Munchkin, Snow Queen, Sykes Dwarf, Pee Wee. If need, prune after flowering to size and shape desired. In early spring remove any winter kill branches or weak branches anytime. Wait till spring buds to show what is dead/alive.
Hydrangea macrophylla – Blushing Bride, Bloomstruck, Endless Summer, Summer Crush, Twist & Shout. Newly planted shrubs usually die back to the ground the first two years until established, so prune down stems each spring when you see new growth coming from the ground. Once established they need little pruning since they also bloom on new wood, with exception of shaping, sizing, and cutting winter kill branches in spring. Wait till you see bud growth on stems. Remove spent or faded flowers just below head all season to promote fresh flowers. Too much pruning during growing season will reduce blooming.
Some Hydrangeas that bloom on new wood:
Hydrangea arborescens – Annabelle, Incrediball, Invincibelle Spirit, Limetta, Mini Mauvette, Wee White.
Hydrangea paniculata – Quick Fire, Limelight, Little Lime, Little Quick Fire, Pink Diamond, Pinky Winky, Tardiva, Vanilla Strawberry, Bobo, Firelight, Strawberry Sundae.
Prune in fall or in spring once buds appear. If you like a clean look for winter, prune off the dried flowers and shape in fall. For winter interest, leave spent flowers till spring. Wait for buds to appear on stems, then prune off winter kill and shape. Remember there are many varieties of Hydrangeas, choose the one that best fits your location for size at total height. To avoid constant pruning of a 6’ plant down to 4’. If need, it is safe to prune 1/3 off if the plant is too large.
The general rule of pruning is that no pruning is better than the wrong type of pruning.
