Even seasoned gardeners seem to be confused as to when to prune Hydrangea.
Begin by identifying which Hydrangea species you are growing, to determine whether it will bloom on new growth or on old wood (last year’s stalks). The species arborescens, paniculata and some newer forms of macrophylla bloom on new wood. All the Hydrangea macrophylla (Mophead and Lacecap types) and quercifolia (Oakleaf) bloom on old wood, as long as there isn’t winter damage. Next year?s blossoms are set on the upper portion of the woody stalks in late summer and fall. H. macrophylla selections should not be pruned until after the plants have leafed out. In late spring, prune out or tip back any dead wood for a clean appearance.
The hardiest and most foolproof of all the Hydrangea are the paniculata group (Pee Gee types) and the arborescens group (Smooth Hydrangea). Both of these species can be cut within inches of the ground each spring if you want to control the size of your plants. They stalks can always be thinned to improve plant shape, and there is no harm to next year’s display if you want to cut long stemmed bouquets in summer and fall.
There are a lot of new Hydrangea macrophylla selections on the market, including ‘Double Expressions’, ‘Red Sensation’, ‘Let’s Dance Starlight’, and ‘Endless Summer’ that bloom on old and new wood. The blossoms appearing on old growth will display in early summer, while the flowers that form on new growth will appear later in August and September, for a long continuous display. If you live in the colder parts of zone 6 or zone 5, you may get too much winterkill for blossoms on the old growth, but you will still be able to enjoy a late summer through fall display.