Hydrangeas do not require pruning. Gardeners can prune hydrangeas if the plants have outgrown their spaces or if they have grown unruly and need shaping. The right time to prune a hydrangea depends on its type.
For some hydrangea varieties, the flowers grow on old wood (branches that grew during the blooming season before the current one). These should be pruned right after the flowers fade. The most commonly grown variety, big-leaf hydrangea, fits into this category.
Other types of hydrangeas have flowers that grow on new wood (branches that emerge during the current growing season). This type should be pruned at the beginning of the growing season, before it flowers.