Endless Summer Hydrangeas are popular for their continuous blooms throughout the growing season. They are unique among bigleaf hydrangeas, blooming on both old and new wood for an extended display of colorful blossoms. While generally robust and adaptable, unexpected temperature drops, particularly late spring or early fall frosts, can threaten their delicate new growth and developing flower buds. Understanding how frost impacts these hydrangeas is important for maintaining their health and ensuring a consistent floral show.
Identifying Frost Damage Signs
Leaves affected by frost often appear wilted, turning dark brown or black, and may feel crispy. Discoloration may also appear as a reddish or purplish hue before darkening.
Flower buds, which are sensitive, will turn brown or black and fail to open. A sudden drop in temperature below freezing can render developing buds lifeless. Stems might also show damage, appearing discolored, soft, or blackened, especially at their vulnerable tips. Symptoms may take several hours or days to fully manifest.
Understanding Endless Summer Hydrangea Susceptibility
Endless Summer Hydrangeas are hardy in USDA zones 4 to 9, but are vulnerable to frost damage during certain periods. Their reblooming nature, producing flowers on both old and new wood, makes them vulnerable. This dual blooming can lead to early bud development on old wood during warm spring temperatures.
If a warm spell initiates budding, a sudden temperature plummet below freezing makes tender new growth and emerging buds highly susceptible to damage. Their extended blooming season into fall also means new growth is active when early autumn frosts arrive, leaving it exposed. Unlike some other hydrangeas that only bloom on new wood and can be cut back without losing the season’s flowers, Endless Summer’s reliance on both old and new wood means frost damage to early buds can significantly impact the initial flush of blooms.
Preventing Future Frost Damage
Regularly monitor local weather forecasts to anticipate frosts. Before a cold snap, hydrate plants adequately; moist soil retains heat better, insulating roots.
Apply a 2 to 3-inch layer of mulch around the plant’s base to insulate the root system. Keep mulch a few inches from the main stem to prevent rot. When frost is predicted, cover plants with burlap, frost cloths, or old sheets. Extend covering to the ground to trap warmth, removing it once temperatures rise above freezing for air circulation and sunlight. Selecting a planting site that avoids “frost pockets”—low-lying areas where cold air settles—reduces damage.
Steps for Recovery After Frost
Wait to assess the full extent of damage before pruning. Immediate pruning can expose the plant to further damage if another cold event occurs, and depletes energy reserves needed for recovery.
Once frost danger has passed, typically in mid to late spring, remove damaged portions. Prune back affected stems to healthy wood, cutting just above a healthy bud or set of leaves. Determine healthy wood by scraping the bark; green tissue indicates living wood, while brown or dry tissue signifies damage. Provide supportive care, such as consistent watering and avoiding excessive fertilization, to encourage new growth and potential blooms later in the season. While the initial flush of flowers may be reduced, Endless Summer Hydrangeas often recover and produce blooms on new wood.