How to prune Annabelle and mophead hydrangeas
A lot of confusion exists around when and how hydrangeas can be pruned but once a hydrangea is correctly identified, pruning becomes fairly easy.
The nickname mopheads (H. macrophylla) is descriptive of the shape of their blooms. Blue, pink and purple are the most common colours. White is fairly uncommon. If the blooms on your hydrangeas are white, consider the possibility that they are not macrophyllas but are one of the other species.
Mophead hydrangeas do not have to be pruned back unless they are very old. Removing dead stems and blooms is the only pruning that should be done for the health of the plant, and these can be removed at any time. But if your hydrangea is getting much too large or old, use the following method.
These hydrangeas bloom on old wood. (Stems that have been on the hydrangea since the summer before the current season.) They produce flower buds in August, September or October for the following summer’s blooms. If those stems are pruned in the fall, winter, or spring, the bloom buds will be removed, and there may be little or no bloom the following summer (usually June/July for the northern hemisphere).
Unfortunately H. macrophylla is the variety most susceptible to winter bud injury in Southern Ontario. Our winters can be severe, so you might need to offer it some winter protection from severe winds to protect the flower buds. Tying the branches together and wrapping them with burlap isn’t pretty, but it could mean winter survival. Remove the burlap when the buds begin to swell.
‘Annabelle’ is one variety in the species H. arborescens. Its blooms may bring lollipops to mind. They are usually very large, and made up of tiny individual blossoms. There is one trait that sets ‘Annabelle’ apart from most other hydrangeas – the blooms open green, turn white for 2-3 weeks, and gradually turn green again (at which time they can be used in dried arrangements). These huge blooms are notorious for falling over in wind and rain storms.
H. arborescens bloom on new wood.( Stems that developed on the plant during the current season) So late winter or early spring is the time to prune. Just look for the first set of fat new buds and prune back the stem to just above this new growth. If you have a lusty plant and want to keep it contained, you can cut back drastically — almost to the ground — in late winter before the new growth appears. Or you can leave more of the woody stem in order to give the heavy heads more support. Cut any dead branches to the ground at any time; they’ll be brittle, so easy to identify.