Hydrangeas are some of the most beautiful as well as durable shrubs in our gardens. Even as the blooms dry they look spectacular on the bushes in late fall and winter, and they’re attractive dried in vases as well as in decorative wreaths.
Hydrangeas can be classified a number of different ways but a useful distinction is which shrubs bloom on old or new wood ( i.e. last year’s branches or those produced this year). This distinction is important because if one of your shrubs blooms on old stems and you cut it back this fall, you will get no blooms next year. On the other hand, if you own a type of hydrangea that blooms on new growth, you could prune it this fall and it will have time to grow new stems and bloom next year (probably by late summer or fall).
The types that bloom the earliest in the calendar year usually bloom on old stems. This makes sense since the buds, already inside the old wood, will be all set to go when it gets warm enough next year. That is, as long as a late spring freeze does not ruin them, as sometimes happens. This is what happened if you get no blooms, or just one or two at the bottom of the bush where the stems have been protected by leaves or upper branches.
Generally, the ones that bloom on their existing branches early in the year are, for example, the Hydrangea macrophylla (the big-leaf hydrangeas), Hydrangea serrata (the lace-cap hydrangeas), and Hydrangea quercifolia (the oak-leaf hydrangeas). Prune these immediately after the blooms have faded. Remove any dead canes, but never prune them to the ground.
Late year bloomers on new wood are Hydrangea paniculata (Panicle hydrangeas) Hydrangea arborescens (Smooth), and the climbing hydrangeas. Cut back these in late winter before new growth begins. Hydrangea arborescens can be cut to the ground in late winter, which will stimulate larger flowers and better form.