Hydrangeas are popular garden shrubs known for their large, showy clusters of flowers. While famous for their blooms, they do not flower all year long, as their blooming is tied to the annual growth cycle. Depending on the species and variety chosen, the season can extend from early summer well into the fall months. Understanding a hydrangea’s growth habit is key to maximizing its flowering display throughout the warmer seasons.
The Difference Between Old Wood and New Wood
The factor determining a hydrangea’s bloom time and care is whether it flowers on “old wood” or “new wood.” Old wood refers to stems grown during the previous season, where the plant develops flower buds in the late summer or fall. These pre-formed buds must survive the entire winter to bloom the following summer.
Conversely, new wood is the fresh growth that emerges in the current season, typically in the spring. Hydrangeas that bloom on new wood create their flower buds on these fresh stems after the plant breaks dormancy. This difference dictates when a plant flowers and when it can be safely pruned without removing the next season’s potential blooms.
The distinction also affects winter hardiness, as exposed old wood buds are susceptible to damage from late spring frosts or severe cold. New wood bloomers are more reliable in colder regions because the flower buds do not form until the weather warms.
Bloom Timing for Common Hydrangea Types
The four most common species of hydrangeas each have a distinct blooming schedule based on their wood type. The Bigleaf Hydrangea (Hydrangea macrophylla), including Mophead and Lacecap varieties, blooms on old wood. These plants typically provide a single flush of color in early to mid-summer.
Oakleaf Hydrangea (Hydrangea quercifolia) also blooms on old wood, generally flowering in early summer, often preceding the Bigleaf varieties. Both types have flower buds present on the stems throughout the winter.
In contrast, Panicle Hydrangea (Hydrangea paniculata) and Smooth Hydrangea (Hydrangea arborescens) bloom on new wood. The Panicle variety, which includes cultivars like ‘Limelight’, begins its display in mid-to-late summer and continues into the fall. Smooth Hydrangeas, such as ‘Annabelle’, reliably bloom from early summer until early fall.
New wood bloomers offer a longer and more consistent flowering period because their bud development is not threatened by winter weather. This makes them a more dependable choice for gardeners in areas with unpredictable temperatures.
Reblooming Varieties and Extended Seasons
Modern breeding efforts have introduced a category of shrubs known as “reblooming” or “remontant” hydrangeas, which offer the longest possible season of flowers. These are typically specific cultivars of the Bigleaf Hydrangea (H. macrophylla) that have been engineered to produce flowers on both old wood and new wood. This ability ensures that even if the old wood buds are damaged by cold, the plant will still produce a subsequent flush of blooms later in the season on its new growth.
Cultivars in the ‘Endless Summer’ and ‘Twist-n-Shout’ series are well-known examples of this advancement. These varieties first flower on their old wood in early summer, followed by continuous waves of new blooms throughout the summer and into the early fall. This extended period of flowering, often lasting until the first hard frost, gives the appearance of near all-season blooming. Deadheading, which is the removal of spent flower heads, can often encourage a faster rebloom in these modern varieties.
Essential Care for Maximum Flower Production
Achieving a profusion of blooms requires specific care tailored to the plant’s wood type. Pruning timing is the most frequently misunderstood practice and the most common reason for a lack of flowers. Hydrangeas that bloom on old wood must only be pruned immediately after their summer flowering period ends, typically by late July. Pruning these varieties in the fall, winter, or spring will remove the developing flower buds and eliminate the next season’s blossoms.
For new wood bloomers, pruning should be done in the late winter or very early spring before new growth begins. Since they form buds on the current year’s stems, hard pruning at this time encourages vigorous new growth, which leads to a greater number of blooms. Most hydrangeas thrive in morning sun with afternoon shade, which protects them from the intense heat that can cause wilting or scorch the leaves. Consistent moisture is also paramount, as the name Hydrangea is derived from Greek words meaning “water vessel,” indicating their preference for damp soil.