Hydrangeas are popular flowering shrubs that require specific care to survive the winter and produce robust blooms the following season. Winter is a period that requires deliberate preparation to protect the plant’s structure and developing flower buds. Proper winterizing ensures the plant enters a healthy dormancy, protecting it against harsh temperatures, drying winds, and damaging freeze-thaw cycles. Taking the appropriate steps yields a rewarding display of flowers when the weather warms.
Transitioning Hydrangeas into Dormancy
Preparation for winter begins in late summer or early fall by signaling the plant to cease active growth. The most important step is stopping all nitrogen-rich fertilization by mid-to-late summer, typically no later than early August. Continued feeding encourages soft new growth that lacks the hardiness to survive a frost, leaving the plant vulnerable to winter damage.
As temperatures begin to drop in the fall, gradually reduce watering, but do not stop it entirely. Hydrangeas benefit from deep hydration a few times in the fall to combat the drying effects of winter winds, which can desiccate the stems. Ensuring the root system is adequately moist before the ground freezes helps the stems endure the cold.
Cleanup of the area surrounding the plant should occur before the first hard frost. Removing fallen leaves, spent blooms, or diseased debris minimizes hiding spots for pests and reduces the chance of fungal diseases developing. This allows the plant to focus its energy on preparing for dormancy.
Essential Cold Weather Protection
Physical protection is necessary, particularly for Bigleaf hydrangeas (Hydrangea macrophylla) and other varieties that set their flower buds on old wood. These buds are susceptible to damage from extreme cold or fluctuating temperatures, especially below 0°F. The first layer of defense is applying a heavy, insulating mulch around the crown and base of the plant.
Apply the mulch layer once the ground has started to freeze, not before, to avoid attracting rodents or encouraging premature new growth. Use materials like shredded leaves, straw, or pine needles, building a mound approximately 6 to 12 inches high over the root zone. This organic layer insulates the roots and protects them from frost heave, which is caused by repeated freezing and thawing cycles.
In colder climates, vulnerable varieties may need additional above-ground protection for the canes. Techniques include loosely wrapping the shrub in burlap or creating a chicken wire cylinder filled with dry, insulating material like shredded leaves or straw. Container-grown hydrangeas should be moved to a cool, unheated, and sheltered location like a garage or shed before the first hard freeze.
Understanding Winter Pruning Needs
The winter pruning strategy depends entirely on whether the specific variety blooms on “old wood” or “new wood.” Varieties that bloom on old wood, such as Bigleaf (H. macrophylla) and Oakleaf (H. quercifolia), form their flower buds on the previous year’s growth during late summer. Pruning healthy stems on these types during winter will remove the next season’s flower buds, resulting in a lack of blooms.
For old wood bloomers, winter pruning should be limited to removing dead, broken, or diseased canes, cutting them back to the ground. The dried flower heads can be left on the plant, as they provide protection to the terminal buds just below them. This minimalist approach preserves the buds that have already formed for the next season.
In contrast, “new wood” bloomers, like Panicle (H. paniculata) and Smooth (H. arborescens) hydrangeas, develop their flower buds on the fresh growth that emerges in the spring. These varieties are more forgiving, as late-winter or early-spring pruning will not sacrifice the coming season’s flowers. The only necessary winter task is removing any unsightly spent blooms or damaged branches. While new wood bloomers tolerate hard pruning, it is best saved for late winter or early spring just before new growth starts.