The iconic bigleaf hydrangea, Hydrangea macrophylla, and related mountain hydrangea, H. serrata, that adorn many landscapes on Cape Cod will have less blooms this summer. The bigleaf hydrangea and to a lesser extent mountain hydrangea suffered widespread winter injury because of extreme cold temperatures. The plants will survive but in many cases the stems were killed to or near ground level.
Bigleaf hydrangea is a showstopper of a flower with massive pink to blue inflorescences (Fig. 1). Bigleaf hydrangea is Iconic to the Cape area and even celebrated during the annual Cape Cod Hydrangea Festival. This year however there will be less blooms to celebrate. Bigleaf hydrangea initiates flowers the fall of the previous season in buds on old wood. The overwintering buds and stems are susceptible to being damaged by winter weather extremes. The stems of bigleaf hydrangea have a maximum hardiness of 1°F to -11°F depending on cultivar.
On February 4, 2023, temperatures remained below 0°F for more than ten hours and reached an extreme low of -8°F, in Barnstable, MA. The extreme low temperature has resulted in widespread stem damage to bigleaf hydrangea and therefore flower bud loss (Fig. 2 & 3). The damage is limited to bigleaf hydrangea and mountain hydrangea. Other hydrangea species that commonly occur in the landscape such as smooth hydrangea (H. arborescens), panicle hydrangea (H. paniculata), and oak leaf hydrangea (H. quercifolia) will not be impacted.
Some newer cultivars of bigleaf hydrangea referred to as remontant can produce blooms on old and new wood. Cultivars in the Endless Summer series, Let’s Dance series, and Tuff Stuff hydrangeas are some cultivars capable of blooming on new wood and old wood. The blooms on remontant cultivars typically develop much later than blooms on old wood, typically not appearing until late summer or fall. For cultivars that bloom on only old wood, hope for better luck next winter.
The damaged hydrangeas do offer a good opportunity to get into older shrubs that produce a lot of stems and do some clean-up. Use loopers to remove dead stems near the base or to a point in which buds or shoots are healthy and have begun to grow (Fig. 4 & 5). The removal of dead stems will help provide space for new vigorous shoots to develop which will produce next year’s blooms.
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