Hydrangeas are popular garden shrubs known for their abundant, colorful blooms. Their successful flowering depends on understanding whether they bloom on “old wood” or “new wood,” which refers to the age of the stem that produces the flower bud. Pruning an old wood hydrangea at the wrong time will inadvertently remove the developing flower buds, resulting in few or no blossoms. Knowing the specific type of hydrangea you have is the first step toward ensuring a spectacular floral display the following season.
Identifying Old Wood Hydrangea Varieties
Old wood is the growth that developed during the previous growing season; the plant sets its flower buds on these mature stems for the following year. The most common old wood varieties include Hydrangea macrophylla, widely recognized as the Bigleaf Hydrangea, which comes in Mophead and Lacecap forms. Another prominent member is Hydrangea quercifolia, known as the Oakleaf Hydrangea, easily identified by its lobed leaves and exfoliating bark. The smaller Hydrangea serrata, or Mountain Hydrangea, also blooms on old wood. Conversely, varieties like Hydrangea paniculata (Panicle) and Hydrangea arborescens (Smooth) flower on new wood, requiring a completely different pruning schedule.
When and Why to Prune Old Wood Hydrangeas
The timing of pruning for old wood hydrangeas is specific because the flower buds for the next year are formed shortly after the current year’s blooming period ends. Pruning must occur immediately after the flowers fade, typically from early to mid-summer, generally before late July or early August. This narrow window allows the plant sufficient time to recover and develop the new stems that will host the next season’s flower buds before winter dormancy. The primary purpose of this summer pruning is deadheading, or removing the spent blooms, and maintaining the overall shape and size of the shrub. Pruning past mid-summer risks cutting off the forming buds, sacrificing the next year’s blooms.
Routine Pruning Techniques
Routine maintenance focuses on removing spent material and thinning the plant to encourage healthy new growth and better air circulation. When deadheading, remove the spent flower head by cutting the stem just above the first healthy, outward-facing set of leaves or buds. This careful placement ensures the cut is made safely above the new buds that are beginning to form below the spent flower. Removing any dead, diseased, or damaged stems should be done first, cutting them cleanly back to the base of the plant. A simple scratch test on the stem can confirm viability: if green appears beneath the bark, the stem is still alive.
For shaping and size control, the goal is to thin the plant selectively rather than shear it uniformly. Remove a few of the oldest, thickest, and least productive stems by cutting them down to the ground. This type of thinning rejuvenates the shrub by stimulating fresh growth from the base. Follow the “one-third rule,” which means removing no more than one-third of the total live stems in any given year to avoid stressing the plant or reducing the next season’s bloom potential. Always use sharp, clean bypass pruners to make precise cuts, which helps prevent tearing the wood and reduces the risk of introducing disease.
Dealing with Overgrown or Damaged Hydrangeas
Severely overgrown or neglected old wood hydrangeas may require a more aggressive approach known as rejuvenation pruning, which should still be performed in the summer after flowering. This technique involves removing about one-third of the oldest, woodiest stems each year for three consecutive years. By spreading the heavy pruning over this period, you gradually reduce the shrub’s size while still preserving enough old wood to ensure some flowers bloom each season.
When dealing with winter damage or frost kill, resist the urge to prune in late winter or early spring. Late frosts can damage the tender flower buds at the tips of the stems, but the entire stem may not be dead. Wait until the plant has fully leafed out in the spring and you can clearly see where the new growth begins. At that point, only prune back the damaged stem tips to the first set of visible, healthy buds or leaves. Allowing the plant to show you which parts are truly dead ensures you do not accidentally remove viable stems that would have produced flowers later in the season.