When and How to Prune Hydrangeas
Before grabbing the pruning tools, it is important to identify which species you have. There are six species of hydrangeas that are commonly grown in American gardens and all of them have very different growth habits and pruning requirements.
Hydrangea macrophylla Bigleaf Hydrangea
Native Range: Japan
Old-fashioned varieties of bigleaf hydrangea flower on old wood (the previous year’s growth) and require no pruning.
Dead flowers can be cut off at any time of year.
Because bigleaf hydrangeas bloom on old wood, flower buds are sensitive to a sudden freeze after a period of warm temperatures in the spring. If those buds are damaged, the shrub may not produce flowers.
The first bigleaf hydrangea to bloom on old and new wood, was introduced in 2004, extending the bloom season. This introduction enables plants to bloom regardless of winter damage or pruning mistakes. “Bigleaf hydrangeas that bloom on old and new wood are known as reblooming, or remontant, hydrangeas, since they bloom first on their old wood, then after a brief rest for some vegetative growth, create flower buds on that new growth that open in the following weeks”, as described on the website Hydrangeas.com.
All varieties of bigleaf hydrangea should be pruned to remove dead canes (stems). Cut these down to the ground.
Hydrangea arborescens Smooth hydrangea
Native Range: Eastern North America
Smooth hydrangeas bloom on new wood and will tolerate heavy pruning. Cut a third of the oldest stems to 24” each year in late winter to early spring. This will eliminate a top-heavy shrub that flops to the ground by midseason by providing a frame that helps to hold up new stems, and contribute to robust flowering.
Hydrangea paniculata Panicle hydrangea
Native Range: southern and eastern China, Korea, Japan and Russia
Panicle hydrangeas bloom on new growth and should be pruned in late winter to early spring before its leaves emerge. You can prune just below each flower head, basically ‘dead-heading’ the shrub. Or, because this species of hydrangea blooms on new growth, it can be pruned moderately to make the shrub smaller, or pruned severely to rejuvenate.
Hydrangea quercifolia Oakleaf hydrangea
Native Range: Southeastern part of the United States
Oakleaf hydrangeas are usually the first hydrangeas to bloom in early summer. They flower on new wood and typically do not rebloom. As a rule, oakleaf hydrangeas do not require much pruning. If you prefer to tidy it up, remove the dead flower heads just under the bloom.
Remove dead or damaged branches any time of year.
Hydrangea anomala ssp. petiolaris Climbing hydrangea
Native Range: the woodlands of Japan, the Korean peninsula, and on Sakhalin island
Climbing hydrangea is a vining species that grows up structures with aerial rootlets along its stems that allow the branches to climb. This species blooms on old wood and can be pruned in summer, after flowering. However, pruning is not required other than to remove dead or damaged stems.
Hydrangea serrata Mountain hydrangea
Native Range: mountainous regions of Korea and Japan
Mountain hydrangeas look very similar and are closely related to bigleaf hydrangeas. Flowers develop on old wood. Reblooming types are increasingly available and provide more reliable blooms.
Cut back winter-damaged stems in early spring.