Pruning hydrangeas is one of those subjects that makes many gardeners nervous. Part of the problem is that the various kinds of hydrangeas grow and bloom in different ways on different schedules. It can be confusing trying to figure out just which kind of hydrangea you have in your garden and how and when it should be pruned and fertilized.
Most mopheads, for instance, set new buds every year on old wood—as in wood from the previous growing season—which means that when spring comes, the coming summer’s flowers have already appeared as buds ready to bloom in late June or early July. This means that if you decide to prune your mopheads and lacecaps in April—which you should do at that time of year to get rid of any dead, diseased, or under-performing canes—you need to be careful not to cut off the healthy buds that matured over the previous growing season, or you won’t have any flowers come summer.
Hydrangea paniculatas, including “Pee Gees,” “Limelights,” “Little Lime,” and so forth, do not bloom on old wood, but set their flower buds in the spring on new wood. This means that you can prune any dead or diseased canes without worrying about cutting off the flowers for this season’s blooming. Paniculatas can be pruned in April along with the macrophyllas, although it is better to prune the paniculatas even earlier in late February or March.
Cape Cod Hydrangea Society
A good resource is the Cape Cod Hydrangea Society (capecodhydrangeasociety.blogspot.com), an organization of dedicated hydrangea growers who all have years of experience. The society’s meetings are very helpful and feature informative presentations by hydrangea growers, floral designers, landscaping professionals, and others.
The society is also responsible for a beautiful hydrangea display designed and planted six years ago at Heritage Museums and Gardens. An annual society membership is $25. If you want to learn everything there is to know about hydrangeas, this is the organization to join.