I’m not sure that pruning your blue hydrangeas will ruin them, although you might not see as many blooms next year. The way you prune hydrangeas depends on the type of hydrangea and how it blooms.
Some types (such as yours) bloom on old wood, so they shouldn’t be pruned severely other than to remove dead branches. Other types bloom on new wood, so some strategic pruning can help them thrive.
Here are some tips for pruning the hydrangeas in your yard.
- Mophead or Lacecap Hydrangeas: (Hydrangea macrophylla) All hydrangeas with colored flowers (pink, purple, and blue) fall in this category, as well as some types of white hydrangeas. These types of hydrangeas don’t need to be pruned at all, other than deadheading and removing dead branches. Since they bloom on old wood (rather than this year’s new branches), excessive pruning of mophead or lacecap hydrangeas will reduce blooming. If your plant is overgrown and must be trimmed, do it before August, when the plant sets next year’s flower buds. If your plants are old and declining, you can revitalize it by removing up to a third of the oldest branches in midsummer, just as the blooms start to fade.
- Oakleaf Hydrangea: (Hydrangea quercifolia) Oakleaf hydrangeas have white blooms and large oak-shaped leaves. They bloom on old wood and should be treated just like H. macrophylla above.
- PeeGee and Annabelle Hydrangeas: (Hydrangea paniculata and Hydrangea arborescens) Both of these hydrangeas have white blooms and bloom on new wood (this year’s new branches). They can be pruned starting immediately after they flower on into fall and winter. Don’t prune in spring or summer when they’re preparing to bloom. You can prune lightly or severely, depending on the size and shape you want. These hydrangeas don’t have to be pruned at all, but some gardeners cut them back each year.