From a botanical perspective, the most critical factor in pruning hydrangeas is understanding their flowering habit, which is determined by the plant's bud development. Hydrangeas form flower buds at specific times of the year, and incorrectly timed pruning will remove these buds, resulting in a season with few or no blooms. The primary distinction lies in whether the plant blooms on "old wood" (growth from the previous season) or "new wood" (growth produced in the current season). This fundamental difference dictates the entire pruning strategy.
These hydrangeas initiate their flower buds in late summer or early fall on the stems that grew that season. These buds must survive the winter on the stem (the "old wood") to open the following summer. Pruning these types in fall or spring will remove the upcoming season's flowers.
Key Species: Bigleaf hydrangeas (Hydrangea macrophylla), including mophead and lacecap varieties, Oakleaf hydrangeas (Hydrangea quercifolia), Mountain hydrangeas (Hydrangea serrata), and Climbing hydrangeas (Hydrangea petiolaris).
Pruning Guide: The ideal time to prune is immediately after their flowers fade in mid-to-late summer. This gives the plant ample time to produce new growth that will mature and set flower buds before winter dormancy. Focus on removing spent flower heads by cutting just above the first set of large, healthy leaves. Also, remove any thin, weak stems at the base and about one-third of the oldest stems to encourage new growth from the root crown, which will rejuvenate the plant over time.
These hydrangeas are more forgiving. They form their flower buds on the new growth that emerges in the spring. Because they start from scratch each year, they can be pruned while dormant without sacrificing blooms. This makes them ideal for colder climates where winter die-back on old-wood bloomers is a problem.
Key Species: Panicle hydrangeas (Hydrangea paniculata) and Smooth hydrangeas (Hydrangea arborescens).
Pruning Guide: Prune these plants in late winter or very early spring, just as new leaf buds begin to swell. For Panicle hydrangeas, which can be trained into small trees, pruning can be quite aggressive. Cut back stems by about one-third to one-half to maintain a strong structure and promote larger flower heads. For Smooth hydrangeas like 'Annabelle', you can practice renewal pruning by cutting all stems back to about 6-12 inches from the ground each year. This encourages vigorous new growth that will support the characteristic large, heavy blooms.
This is a modern category, primarily consisting of reblooming Bigleaf hydrangeas (e.g., the Endless Summer series). From the plant's viewpoint, these cultivars have been bred to flower on both old wood and new wood. This provides a safety net; if old wood buds are winter-killed or accidentally pruned off, the plant can still produce flowers on the current season's growth.
Pruning Guide: The best approach is minimal pruning. Deadhead spent flowers as they fade throughout the season to encourage further blooming. The main pruning should still be done after the first flush of summer flowers. Avoid heavy spring pruning, as this will remove the initial old-wood blooms. If the plant is overgrown, you can selectively remove up to one-third of the oldest stems at the base after the first flowering to thin it out. The plant's dual-flowering nature offers flexibility but does not mean it should be pruned heavily.
