Hydrangeas rarely need pruning, but can be pruned to achieve a desired shape or to promote healthy new growth. To understand how to prune hydrangeas, you'll need to determine whether your hydrangea plant blooms on old wood or new wood. Plants that bloom on old wood only flower on branches developed last season, so deadheading spent blooms at the tips of their canes is the best method of pruning for these types. Plants that bloom on new wood develop flowers on new growth, so they can be pruned heavily, if desired, for size and shaping purposes. Different types of hydrangeas have different pruning needs. After pruning, it's common for a hydrangea to quickly grow back to its former size, so keep that in mind when it comes to your garden space and schedule. We have included additional tips for pruning hydrangeas below.
It's recommended these three species be pruned immediately after flowering, in order to avoid interrupting the blooming process for the following year. Many of these "old-fashioned" hydrangea styles bloom on old wood, so you should trim only diseased and damaged branches for maximum flower production. Each year, keep the hydrangea's size in check by trimming branches back immediately after flowering. Prune no more than one-third of the cane. Flower buds for next year develop along the remaining portion of the cane. With these three species, if you cut back canes harder, or prune them to the ground, you run the risk of severely reducing or eliminating altogether your blooms for next year.
There are varieties of macrophylla and serrata that bloom on new wood, but we still suggest pruning sparingly for maximum bloom impact. Prune out damaged, broken, or crossed branches.