I planted a lot of hydrangeas in my garden last year and would like some advice on pruning.
Judy Bowman, Journey
This is the time to prune most hydrangeas grown in the Chicago area while the plants are dormant. Since your plants are newly planted, there is very little, if any, pruning to do this spring. You should finish this pruning before the plants start growing with consistent warm weather later in the spring. In years past when warm weather came quickly I had to prune some hydrangeas as the buds were just beginning to open. In these situations, I wasn’t able to cut back the bushes as vigorously as I would have liked because they were too far in development. There is still plenty of time this winter to complete this pruning.
Smooth hydrangea cultivars such as Annabelle and Apito (Hydrangea arborescens) respond well to being cut back in the dormant season. I prefer cutting them back at ground level or to a height of about 1 inch. Thick stems drop to ground level to open space at the base for new stems to form. This will result in more compact plants. I’ve found that less vigorously growing varieties like ‘Invincibelle® Spirit II’ are best cut back gently. I’ve trimmed ‘Invincibelle ® Spirit II’ hydrangeas by one-third to one-half with good results. Some of the Anabelle Hydrangeas growing in my garden under oak trees have fared sub-par with annual pruning to ground level. They had more foliage and increased blooms when I stopped pruning them vigorously and trimmed the ends of the branches. Shade and root competition from the trees was limiting the hydrangea’s growth response.
Hydrangea cultivars (Hydrangea paniculata) are commonly grown and respond well to pruning at this time of year. Dwarf varieties need very little pruning to maintain good shape. Larger-growing cultivars like ‘Tardiva’ can be pruned back each year if you want to keep them at a smaller size in your garden. I’ve had good results pruning small flowering hydrangeas to about 3 feet above the ground each year. This keeps the shrubs’ more compact size in the landscape. Cut it back less severely if you want to keep a larger shrub in your garden. I have not had good results when pruning very large hydrangeas that have not been pruned for many years. It is best to work gradually to reduce the size of these plants over three to four years. There are enough varieties available now to choose a plant of a size to suit your needs without extensive pruning.
Oak-leaf hydrangeas (Hydrangea quercifolia) flower on old wood, so it’s best to avoid pruning in winter if you want to get blooms this year. If plants are deformed or overgrown, you may want to prune them more vigorously now to correct their structure and sacrifice blooms in summer.
Bigleaf hydrangea cultivars (Hydrangea macrophylla) generally need very little pruning. Sometimes they are mistaken for soft hydrangeas in season for winter pruning. Newer cultivars such as ‘Endless Summer’ flower on old and new wood. There tends to be more winter dead on these hydrangeas, so you may end up pruning back dead stems later in the spring. If you have a cultivar that blooms on older wood, it may have reduced or no flowering due to winter killing of the stems or wrong hard pruning.
For more tips about plants, contact the Chicago Botanic Garden’s Plant Information Service at [email protected]. Tim Johnson is Senior Director of the Horticulture Department at the Chicago Botanic Garden.