Lacecap type of Hydrangea macrophylla

Hydrangea macrophylla ‘All Summer Beauty’

In the Southeastern U.S. region, wildly fluctuating temperatures this winter will likely destroy or delay spring and summer blooming on bigleaf (mophead) hydrangeas (Hydrangea macrophylla) (USDA hardiness zones 6 – 9). Other hydrangea species, such as smooth hydrangea (H. arborescens), panicle hydrangea (H. paniculata), and oakleaf hydrangeas, should not be affected.

Bigleaf hydrangeas are highly sensitive to wild rollercoaster temperature changes during winter dormancy. Although modern day cultivars possess better cold hardiness, pre-formed spring flower buds are in danger. Mild temperatures push buds to swell, responding to a false spring.

All may not lost! Hardier bigleaf hydrangeas, such as the Endless Summer™ and All Summer  Beauty™ series are also in jeopardy for spring bloom losses. They may still bloom on new spring wood this summer, although flowering may be delayed by several weeks and flower heads may be small and fewer in number.

Still more troubles ahead? Bigleaf hydrangeas often respond to an early spring warm-up by breaking dormancy early and produce new shoots and leaves. Sudden spring freezes may severely damage growing buds. In severe situations several branches or whole plants may not bloom thru the summer months. On well-established shrubs, new buds will form at the base, grow out, and attempt to bloom in late summer and fall.