The way a hydrangea produces its flowers dictates how it should be cared for, especially regarding pruning timing. The distinction rests on whether flower buds develop on “old wood” (growth from the previous season) or “new wood” (fresh growth produced in the current spring). Understanding this difference ensures the plant forms flowers, preventing the accidental removal of buds.
Understanding Old Wood Bloomers
Hydrangeas that bloom on old wood set their flower buds much earlier than the actual bloom season. These buds are formed on the woody stems in late summer or early autumn of the year prior to flowering. The entire plant must survive winter with these pre-formed buds intact for a successful display.
The main species relying on this pattern are Bigleaf Hydrangea (Hydrangea macrophylla) and Oakleaf Hydrangea (Hydrangea quercifolia). Because the flower buds must overwinter, these varieties are more susceptible to damage from late spring frosts or harsh winter temperatures. Blooms generally appear earlier in the season, often starting in early to mid-summer.
Understanding New Wood Bloomers
Conversely, hydrangeas that bloom on new wood delay bud development until the current growing season begins. The plant produces new stems from the base or existing woody growth in the spring. Flower buds then form on the tips of those new shoots, making them more resilient to cold climates since buds do not need to overwinter.
The primary species in this category are Smooth Hydrangea (Hydrangea arborescens) and Panicle Hydrangea (Hydrangea paniculata). Since the plant must first grow the stem and then form the bud, these varieties tend to bloom later in the summer, typically starting in mid-July. Even if the plant dies back to the ground during a severe winter, it can still produce flowers that same season.
Identifying Your Hydrangea Species
The most definitive way to determine wood type is to check the specific variety or cultivar name. If the original plant tag is available, look for the scientific name, such as H. macrophylla or H. paniculata. Cultivar names can also be helpful; for instance, ‘Annabelle’ is a Smooth Hydrangea, while ‘Limelight’ is a Panicle Hydrangea.
If the name is unknown, visual cues offer the next best method of classification. Panicle Hydrangeas (H. paniculata) are recognized by their distinct cone-shaped or pyramidal flower clusters. Oakleaf Hydrangeas (H. quercifolia) have deeply lobed leaves resembling those of an oak tree, and their bark often peels away in cinnamon-colored strips. Bigleaf Hydrangeas (H. macrophylla) display large, rounded “mophead” flowers or flat-topped “lacecap” blooms.
Smooth Hydrangeas (H. arborescens), such as ‘Annabelle,’ typically have large, white, snowball-shaped flowers and a softer, more pliable stem structure. Remontant cultivars, such as the ‘Endless Summer’ series, complicate identification. These specialized Bigleaf Hydrangeas were bred to bloom on both old wood that survived winter and new wood grown in the current season. This dual-blooming nature ensures flowers even if the previous year’s buds are destroyed by frost.
Pruning Based on Wood Type
For hydrangeas that flower on old wood, pruning must be completed immediately after the flowers fade in the summer. Pruning these varieties after late July risks cutting off the buds that are forming for the following year’s display.
New wood bloomers are much more forgiving regarding pruning timing. Since flower buds do not develop until spring, these varieties can be safely pruned back hard in late winter or early spring before new growth emerges. Pruning at this time encourages vigorous new stem growth and helps maintain the shrub’s shape without sacrificing current season flowers.