Hydrangeas are diverse, and their pruning requirements depend on the species. The two main categories are:
a) Hydrangeas that bloom on old wood: These include Hydrangea macrophylla (bigleaf), H. quercifolia (oakleaf), and H. serrata (mountain hydrangea). They form flower buds in late summer/fall for the next year. Pruning at the wrong time (e.g., late winter/spring) removes these buds, reducing blooms.
b) Hydrangeas that bloom on new wood: Such as H. paniculata (panicle) and H. arborescens (smooth hydrangea). These produce flowers on current-season growth, so pruning in late winter/early spring encourages vigorous new stems and abundant blooms.
Timing is critical to avoid cutting off future blooms:
a) Old-wood bloomers: Prune immediately after flowering (mid-to-late summer). This allows time for new growth to harden off and set buds for next year. Avoid fall/winter pruning.
b) New-wood bloomers: Prune in late winter or early spring before new growth emerges. This stimulates fresh stems that will bear flowers the same year.
c) Reblooming varieties (e.g., Endless Summer): These bloom on both old and new wood. Lightly prune spent flowers in summer, and avoid heavy cuts to preserve old-wood buds.
Proper technique ensures healthy growth and abundant flowers:
a) Tools: Use clean, sharp bypass pruners for precise cuts. Disinfect blades with rubbing alcohol to prevent disease spread.
b) For old-wood bloomers: Remove only dead, damaged, or weak stems. Cut spent flowers just above the first set of healthy leaves. Thin out up to 1/3 of older stems to improve airflow.
c) For new-wood bloomers: Cut stems back by 1/3 to 1/2 in late winter, leaving 2–3 pairs of buds per stem. For H. arborescens, some gardeners prune to the ground annually for larger (but fewer) flowers.
d) Deadheading: Remove faded blooms anytime to redirect energy to new growth, but avoid cutting below the first leaf node on old-wood varieties.
Beyond timing and technique, these factors influence bloom production:
a) Light: Hydrangeas need adequate sunlight (morning sun/afternoon shade for most) to set buds. Over-pruning can reduce foliage, limiting photosynthesis.
b) Fertilization: Apply a balanced fertilizer in early spring. Excess nitrogen promotes leafy growth at the expense of flowers.
c) Winter protection: For old-wood bloomers in cold climates, mulch the base and avoid pruning in fall to protect buds from frost damage.
