Pruning hydrangeas is a practice that directly influences the health, shape, and overall flowering output of the shrub. While the timing of the cut is often discussed, the specific location of the cut—the “where”—is the detail that determines whether the plant will produce a full flush of blooms or none at all. The goal of structural pruning is to remove old, weak, or congested growth to promote fresh, vigorous stems while carefully preserving the microscopic flower buds that are already set for the next season. Understanding the precise placement for each snip ensures the plant can dedicate its energy to maximum flower production.
Why Knowing Your Hydrangea Type is Essential
The fundamental decision of where to cut a hydrangea depends entirely on its species and whether it flowers on “old wood” or “new wood.” Old wood refers to stems grown the previous season; flower buds are set in late summer or fall and must survive the winter to bloom the following year. Conversely, new wood means the stems emerge and form flower buds during the current growing season, blooming in the same year.
Common examples of old wood bloomers are Hydrangea macrophylla (Bigleaf) and Hydrangea quercifolia (Oakleaf). New wood bloomers include Hydrangea paniculata (Panicle) and Hydrangea arborescens (Smooth). Cutting an old wood bloomer at the wrong time will remove the next season’s flower buds, resulting in a healthy but bloomless shrub.
Pruning Hydrangeas That Bloom on New Wood
Hydrangeas that bloom on new wood, primarily H. paniculata and H. arborescens, offer the most flexibility for structural pruning because flower buds have not yet formed. The best time to make these cuts is in late winter or early spring before new growth begins. Pruning these types encourages stronger stems that better support the weight of large flower heads, preventing them from flopping over.
When pruning to reduce the size of the shrub, stems can be cut back aggressively by one-third to two-thirds of their total length. The precise cut should be made just above a healthy, outward-facing bud or a node. For rejuvenation pruning, the oldest and thickest stems can be cut all the way back to the ground to promote fresh, vigorous new growth.
Pruning Hydrangeas That Bloom on Old Wood
Pruning hydrangeas that bloom on old wood, such as Bigleaf and Oakleaf types, requires precision to avoid removing pre-formed flower buds. Structural pruning should be done immediately after the flowers fade, typically in mid-to-late summer, allowing the plant time to set new buds. Pruning these varieties in the fall, winter, or spring will eliminate the next season’s blooms.
The approach for these shrubs is primarily selective thinning and removal of dead material. Any dead, weak, or non-productive canes should be removed completely by cutting them back to ground level. If the shrub needs size control, a maximum of one-third of the oldest stems can be cut back to the base to encourage new growth. When trimming a live cane to manage height, the cut must be made just above a pair of strong, healthy buds.
Removing Faded or Spent Blooms
The process of removing spent flowers, known as deadheading, is distinct from structural pruning and is done primarily for aesthetic reasons or to redirect the plant’s energy. Deadheading prevents the plant from expending resources on seed production and can encourage reblooming varieties to produce new flowers faster. This technique is safe for all hydrangea types and can be done any time the flowers turn brown or fade.
To deadhead correctly, trace the stem of the spent bloom downward to the first set of large, healthy leaves or buds. The cut should be made cleanly just above this healthy node using sharp pruners. Cutting too far down the stem removes potential flower buds, delaying the plant’s ability to set new growth. Gardeners may choose to leave faded blooms on the plant through winter for aesthetic interest and to offer some protection to the delicate buds below.