Hydrangeas that bloom on new wood can be safely pruned in late fall once the plants have gone dormant or in early spring. Next year's flower buds won't be formed until late spring the same year they bloom, so there is no risk of removing the buds if you prune in fall or spring.

What month should I prune my hydrangea?

Trimming should be done immediately after flowering stops in summer, but no later than August 1. Do not prune in fall, winter, or spring or you could be cutting off new buds. Tip-pruning the branches as leaves emerge in spring can encourage multiple, smaller flower heads rather than fewer larger flower heads.

Which hydrangeas should not be cut back?

The four species that flower on old wood—bigleaf, oakleaf, mountain, and climbing hydrangeas—may not need pruning at all, except when you are pruning to keep their size or shape in check.