Hydrangeas are popular shrubs known for their large, colorful blossoms. As seasons change and weather cools, gardeners often wonder how these plants look during winter. The question of whether hydrangeas lose their leaves relates directly to the plant’s natural survival strategy. Understanding this seasonal transformation is essential for proper care during the colder months.
The Deciduous Nature of Hydrangeas
Most cultivated hydrangeas are deciduous shrubs, meaning they naturally shed their leaves once a year. This leaf loss is a physiological adaptation allowing the plant to survive periods when the ground is frozen or water is unavailable. As temperatures drop and daylight hours shorten, the plant enters dormancy, a state of reduced metabolic activity.
The process of shedding leaves is called abscission, controlled by plant hormones like ethylene. A specialized abscission layer forms where the leaf stalk meets the stem. This layer seals off the leaf before it drops, preventing water loss and protecting the stem from open wounds.
By dropping leaves, hydrangeas prevent excessive moisture loss through transpiration when roots cannot absorb water from frozen soil. The plant conserves energy and nutrients by storing them in the roots and stems for the next growing season. This natural cycle results in bare, woody stems throughout the winter months, signaling a healthy and necessary rest period until spring growth begins.
Distinguishing Between Hydrangea Types
While most common garden hydrangeas are deciduous, variations exist, especially in milder climates. The following popular types reliably lose their foliage as they enter winter dormancy:
- Bigleaf hydrangeas (H. macrophylla)
- Panicle hydrangeas (H. paniculata)
- Smooth hydrangeas (H. arborescens)
- Oakleaf hydrangeas (H. quercifolia)
A few species exhibit different tendencies, particularly in warmer regions. The Mexican climbing hydrangea (Hydrangea seemannii) is an exception, classified as an evergreen climber that retains its glossy, leathery leaves year-round. This species is hardy only in very mild climates, such as USDA Zones 7b to 10b, where freezing temperatures are rare.
Mountain hydrangeas (H. serrata) are generally deciduous shrubs, similar to bigleaf hydrangeas but more cold-tolerant. In the mildest parts of their range, they may occasionally behave as semi-evergreen, holding onto some leaves. However, they still drop the vast majority of their foliage, making it necessary to understand the specific species to predict its winter appearance.
Preparing Hydrangeas for Winter
Preparing hydrangeas for their dormant period involves specific actions to safeguard the plant until spring. As leaves drop, the plant’s need for water decreases, but a final deep watering before the ground freezes is beneficial for root hydration. This is especially important in areas with dry winters or significant wind, as the dormant stems can still lose moisture.
Applying a layer of organic mulch is important to insulate the root zone from extreme temperature fluctuations. Spread shredded bark, compost, or wood chips, typically 4 to 6 inches deep, around the base of the plant, extending to the drip line. Avoid piling mulch directly against the stems, which can trap moisture and encourage rot or pests.
Pruning Timing
Gardeners must resist the urge to prune most hydrangeas in the fall or early winter. Pruning at this time can encourage tender new growth that frost will damage, or it may remove the flower buds for the following season. For bigleaf and mountain hydrangeas, which bloom on old wood, pruning should be postponed until after they flower in the summer. Panicle and smooth hydrangeas, which bloom on new wood, are best pruned in late winter or early spring before new growth begins.
Assessing Plant Health During Dormancy
A healthy, dormant hydrangea appears as a collection of bare, woody stems, with any remaining leaves being brown or shriveled. The stems should feel firm and solid to the touch, not brittle or spongy. A simple way to check for life is by performing a scratch test on a small section of a stem.
Using a fingernail or small knife, gently scratch away the outermost layer of bark. A living stem will reveal a bright green layer underneath. If the layer beneath the bark is brown or dry, that portion of the stem is likely dead from winter kill or disease. This test helps distinguish between normal dormancy and actual damage, guiding where spring pruning should occur.
Checking Buds
It is important to observe the color of the buds during late winter and early spring. Healthy buds, particularly on old wood bloomers, should be plump and light green or reddish-green. Buds that appear black, shriveled, or dark brown have likely been killed by cold temperatures or late frost. While some stem dieback is normal, significant bud loss may indicate the need for better winter protection in subsequent years.