Cutting back hydrangeas
How to care for hydrangeas in the fall & winter
There is no special care necessary. Pruning technic and time for hydrangea depends on what type you have. See linked article. If you don't still have the plant tag, refrain from pruning for one year and observe your plant. You need to establish if it blooms on stems formed this year or on new ones that sprout next year. Some of the newer varieties like Endless Summer bloom both on old wood and new wood. If you wish, remove the spent blooms but not the entire stem. Come spring, these dead-looking stems spring to life and it is easy to prune too much and accidentally remove next year's blooms. With all perennials, it is important to water them if autumn or early winter are dry and soil becomes dry. Roots need moisture and a plant that has dried out is much more susceptible to winter kill. Mulch the rootball and crown with several inches of chopped leaves or straw and pull it back from the crown early next spring.