Beloved by gardeners far and wide, hydrangeas nevertheless present some confusion when it comes time for hydrangea pruning. Here are basics that should guide you and help your hydrangea flowers growing healthy and strong.
Hydrangeas can present a bit of a conundrum for gardeners when it comes to pruning, because there's no single method that's right for all hydrangeas. Here are the basics of hydrangea pruning—when to prune hydrangeas, how to prune hydrangeas, and some key hydrangea pruning mistakes to avoid.
When asked why a hydrangea isn't blooming, Vincent Simeone, a horticulturalist, lecturer, and garden writer, is likely to ask about hydrangea pruning practices. "Improper pruning causes a lot of blooming problems," says Simeone, who wrote Great Flowering Landscape Shrubs.
That's because many gardeners don't understand that not all hydrangeas bloom the same way: Some bloom on new wood, and some bloom on the previous year's wood. When pruning occurs at the wrong time, it can eliminate the upcoming bloom.
Pee Gee hydrangea (Hydrangea paniculata, which includes varieties such as 'Limelight') as well as smooth hydrangea (Hydrangea arborescens, also called seven bark and best known for the variety 'Annabelle') bloom on new wood. Timing for the pruning of these types of hydrangea is not as critical, says Simeone. "You can prune in winter or early spring and they will grow and flower in the same season," he says.
Big leaf, or mophead, hydrangea (Hydrangea macrophylla) and oakleaf hydrangea (Hydrangea quercifolia) both bloom on the previous season's growth. "If you prune these at the wrong time of the year, they either won't flower or will flower sporadically," says Simeone. These should be pruned soon after flowering in summer, and never too severely—less than one-third of the plant at any one time, Simeone says.
Some newer varieties of big leaf hydrangea, including the popular 'Endless Summer', have been bred to bloom on new wood as well as old wood. This makes them better for cold climates because even if the old stems suffer cold damage, new growth will still bloom. It also provides more flexibility in pruning. "You can prune it at any time of the year and it should still bloom," says Simeone. Even so, pruning right after bloom will maximize flowering.
When pruning hydrangea, it's best to take off no more than one-third of the plant at any one time. Your objective also determines how you prune it, says Simeone. "If you are just doing some shaping of plants that are too tall, you want to take the top growth down a little," he says. "If you need to do a severe pruning or rejuvenate the plant, you may want to take the branches all the way down to near the ground."