The single most critical factor in determining the best pruning time is the specific type of hydrangea you have, as their flowering wood differs drastically. From a botanical perspective, hydrangeas can be categorized into two main groups based on their bud development: those that bloom on "old wood" and those that bloom on "new wood."
This group includes the popular Bigleaf hydrangeas (Hydrangea macrophylla), which encompass mophead and lacecap varieties, as well as Oakleaf hydrangeas (Hydrangea quercifolia) and Mountain hydrangeas (Hydrangea serrata). These plants initiate their flower buds for the next summer during the previous growing season. The buds form on stems that have matured ("old wood") and must survive the winter. If you prune these stems in fall, winter, or spring, you will be removing the dormant flower buds, resulting in little to no bloom for the upcoming season. The optimal time to prune these varieties is immediately after their flowers fade in mid-to-late summer. This allows the plant ample time to develop new growth that will mature and set flower buds before the plant goes dormant for winter.
This category includes Panicle hydrangeas (Hydrangea paniculata) and Smooth hydrangeas (Hydrangea arborescens), such as the classic 'Annabelle'. These varieties produce flower buds on the current season's new growth. They are far more forgiving regarding pruning time. You can prune them in late winter or very early spring, just as new leaf buds begin to swell. Pruning at this time, while the plant is still dormant, encourages vigorous new growth that will bear that year's flowers. Pruning can also be done in fall after leaf drop, but it leaves the stems exposed to potential winter damage, which is why late winter is often preferred.
A modern development in horticulture is the introduction of reblooming hydrangea cultivars, such as the Endless Summer series. These Bigleaf hydrangeas are unique because they can flower on both old wood from the previous season and new wood from the current season. This dual-flowering capability provides more flexibility. If old wood buds are winter-killed, the plant can still bloom on new growth. For these varieties, a light pruning after the initial flush of flowers in early summer can encourage a second bloom. Major shaping is still best done immediately after the main flowering period.
Regardless of type, the plant's primary needs are for health and structure. The best practice is to always remove dead, damaged, or diseased wood as soon as it is noticed, at any time of year. For all hydrangeas, making clean cuts just above a set of healthy buds promotes proper healing and directs energy for strong new growth. Thinning out a few of the oldest stems each year encourages rejuvenation and improves air circulation within the canopy, which is vital for preventing fungal diseases and promoting overall plant vitality.
