Old wood vs. new wood
Story and Photography by Andrea Dee
Gardeners are sometimes stumped when it comes to pruning hydrangeas. Many gardeners have asked, “When do I prune and why isn’t this thing blooming?” But before you grab the shears, it is important to know if a hydrangea blooms on old or new wood.
Hydrangeas That Bloom on Old Wood
Bigleaf (H. macrophylla), lacecap (H. macrophylla), mophead (H. macrophylla), oakleaf (H. quercifolia), mountain (H. serrata), and climbing hydrangeas (H. petiolaris) bloom on old wood, meaning they set flower buds the fall or winter before bloom. Shorter days and cooler nights help buds develop. If buds are removed in late winter or early spring, you will not see any blooms that summer. Hydrangeas that bloom on old wood should be pruned just after flowers fade in the summer. Generally, shrubs that set floral buds on old wood are spring and early summer bloomers, with a few sporadic blooms later in the summer.
Hydrangeas That Bloom on New Wood
Panicle (H. paniculata), such as peegee, and smooth (H. arborescens), such as ‘Annabelle’, hydrangeas bloom on new wood, usually midsummer until the first frost. These species are much more forgiving. Pruning during the dormant season is easiest since you can see through the canopy to make more selective cuts. Pruning can be done any time from late winter to early spring.
Pruning smooth hydrangeas to the ground can increase bloom size but is likely to decrease stem size, resulting in flopping. Leaving approximately one-third of the old canes will give you a sturdier plant.
Hydrangeas That Don’t Follow Any of the Above – The Rebloomers
Reblooming, technically called remontant, hydrangeas are those that bloom on both old and new wood. If pruning is necessary, the timing shouldn’t affect that year’s blooms. Popular remontant hydrangeas include Endless Summer (‘Bailmer’) and ‘Penny Mac’.
A pair of sharp bypass hand pruners is recommended for most pruning cuts. For mature stems larger than your thumb, a pair of loppers would come in handy. A pruning saw shouldn’t be necessary unless removing fully mature spent canes to the ground level.
Hydrangea bloom size can decrease with age. To rejuvenate tired shrubs, remove the oldest canes back to ground level. Doing so will encourage new, more vigorous growth. To control hydrangea size, simply tip back canes to an appropriate height for your garden space. Cut stems back to a visible bud set to promote new growth.
Pruning hydrangeas is only necessary if shrubs are unsightly or overgrowing their space. To avoid regular pruning, select cultivars that fit your space requirements at maturity. Removing spent blooms and branches each year should be adequate maintenance for most hydrangeas.