Hydrangea pruning is confusing.
To do it properly, insuring flowers for the next year, it is necessary to know the type(s) of hydrangea you have: mop head, lacecap, oakleaf, arborescens, paniculata, climbing or serrata. This sounds daunting, but types can generally be determined by the shape of the flower.
Mop heads are the large-headed, round, blue or pink ones. Lace caps have flat heads, blue or pink, with un-petaled, very small flowers surrounded by larger petaled flowers. Oakleafs have large-ish, white, cone-shaped flowers on tall stems with leaves shaped like oak leaves. Arborescens are the floppy shrubs with very large white flower heads that turn green. Paniculata types have white cone-shaped flower heads. Some of these we call Pee Gees. This also includes tardiva hydrangeas. Climbing hydrangeas really do climb and have white flower heads like lacecaps. And serrata (prezioza…my favorite hydrangea) resemble mop heads but with smaller flowers and smaller leaves—its flowers are all different shades of blue to pink on the same shrub!
From these, there are three categories of hydrangea, and this determines when and how they are pruned. In the first category are those hydrangeas that form flower buds the year before they bloom. They bloom on “old wood.” In the second category are those that form flower buds the same year they bloom. They bloom on “new wood.” The third category features those that bloom on both new and old wood.
Mop heads, lacecaps, oakleafs, serrata and climbing hydrangeas bloom on old wood. I remove flower heads on this type if they become very ugly; otherwise I leave them on until spring. I do not like to prune them past the second pair of buds and have found that trying to reduce these shrubs, some of which want to become 6’–8’ tall, doesn’t work very well. In spring, I deadhead them and remove any dead wood. If the shrub is congested with branches, I will remove some of the old ones to allow for air movement.
Climbing hydrangeas, however, often need to be pruned during the season to contain their growth, which is vigorous starting about three years after planting. Some flowers might have to be lost.
In the second category, paniculata and arborescens both bloom on new wood. Pruning concepts regarding these hydrangeas, in my experience, vary more widely from gardener to gardener. They are pruned in late winter or early spring. I work for two landscape designers who want them reduced by only a third. In my experience, this method produces more, but smaller, flowers.
When left to my own devices, I prune these to the ground every early spring, leaving one or two buds. Using this method, I have grown Limelight hydrangeas (my second favorite hydrangea) that produced heads that were often 12” tall and 10” in diameter. They looked like clouds on stems. This technique does not keep the shrub short. They come back larger each year. Granted, the method is scary—a big shrub is cut to the ground! Some clients need proof that it really works.
In the third category of hydrangeas are the repeat bloomers. It is impossible to tell this kind from the shape of the flowers—you just need to observe that they bloom in spring and again in late summer. The first flowers will be inside the shrub when the new ones begin to bloom. These need only deadheading and dead wooding, with removal of some older wood to allow for air circulation.
All this said, given the beating the hydrangeas have taken for the last two years, I am pruning mop heads minimally this year—just this gardener’s
Jeanelle Myers is a professional gardener, landscaper and consultant. For gardening discussion you can call her at 631-434-5067. jeanellemyersfinegardening.com