A common issue for gardeners is a hydrangea shrub covered in foliage but producing no flowers. This problem usually stems from misunderstanding when the plant forms its flower buds. Hydrangeas are not uniform, and knowing the specific blooming habit of your plant is the only way to ensure successful flowering year after year and implement the correct care routine.
What is Old Wood Blooming vs. New Wood Blooming
The difference between a hydrangea that blooms on old wood and one that blooms on new wood is the timing of flower bud development. Old wood refers to the stems that grew during the previous summer’s growing season. A hydrangea that flowers on old wood sets its buds in late summer or early fall, and those tiny, undeveloped buds must survive the entire winter to open as flowers the following summer.
New wood describes the fresh stems that emerge in the current spring. Hydrangeas that bloom on new wood form their flower buds during the current growing season, and the blooms appear on those same new stems a few months later. Pruning at the wrong time of year will inadvertently remove the flower buds, resulting in a healthy but flowerless shrub.
Identifying Blooming Habits by Hydrangea Species
Identifying the botanical species name is the most reliable method for determining a hydrangea’s blooming habit. The two primary species that bloom on old wood are Hydrangea macrophylla (Bigleaf Hydrangea) and Hydrangea quercifolia (Oakleaf Hydrangea). Bigleaf hydrangeas produce globe-shaped “mophead” or flatter “lacecap” flowers, forming buds on the previous year’s growth in late summer. Oakleaf hydrangeas are recognized by their lobed, oak-shaped leaves and peeling, cinnamon-brown bark, and they also bloom exclusively on old wood.
The two species that bloom on new wood are Hydrangea paniculata (Panicle Hydrangea) and Hydrangea arborescens (Smooth Hydrangea). Panicle hydrangeas are the most cold-hardy type, producing cone-shaped flower heads and setting buds on the current season’s growth in the spring. Smooth hydrangeas, such as the ‘Annabelle’ cultivar, also bloom on new wood and are known for their large, rounded flower clusters.
Physical Markers and Observation
When the species name is unknown, gardeners can look for physical markers on the plant, especially in late winter or early spring. Old wood stems are thicker, tougher, and possess a gray or brown, woody texture. New wood is more flexible, soft, and retains a greenish tinge.
In late fall or early winter, old wood bloomers can be inspected for viable flower buds, which appear as slightly enlarged, firm nodes along the stem. New wood bloomers do not exhibit these pre-formed buds. If a hard spring frost kills the tender buds on old stems, new green leaves may emerge only from the very base of the plant.
Pruning Timelines Based on Blooming Habit
The pruning schedule must align with the plant’s natural formation of flower buds. For old wood bloomers, such as Bigleaf and Oakleaf hydrangeas, any necessary pruning must be completed immediately after the plant finishes flowering in the summer, before August 1st. Pruning at this time allows the plant sufficient time to grow new stems and set the next year’s flower buds before winter. Pruning old wood bloomers in the fall, winter, or spring will remove the dormant buds and eliminate the following season’s flowers.
New wood bloomers, including Panicle and Smooth hydrangeas, develop flower buds only on current growth. These hydrangeas should be pruned in late winter or early spring while the plant is dormant, before new growth begins. This timing allows the gardener to shape the shrub, remove older wood, or cut the plant back hard without sacrificing the upcoming season’s blooms.