Panicle and smooth hydrangeas flower on new wood (growth created in the current season). Flower buds on these hydrangeas form after the plant leafs out in spring, and open a few months later in summer. As a result, these plants flower reliably each year, no matter how cold the winter was.
Bigleaf, mountain, oakleaf, and climbing hydrangeas flower on old wood (growth created in the previous season). Flower buds on these hydrangeas begin to form in late summer and must remain undisturbed all through the fall, winter, spring, in order to flower the following summer. As a result, these plants will not flower if:
- They are pruned. Pruning at any time will remove potential flower buds.
- They are browsed by deer, which will eat the flower buds.
- They are damaged by weather. Winter weather isn’t actually the problem; rather, it is in spring, when several days of warm temperatures are followed by a sudden freeze, that flower buds are most likely to be damaged.
Reblooming hydrangeas, also known as remontant hydrangeas, are types of bigleaf and mountain hydrangeas that have the unique ability to flower on both old and new wood. Even if the buds are damaged in winter weather, the plant can still flower on wood it produces that season. Reblooming hydrangea varieties include the Let’s Dance series, and Tuff Stuff.