The timing and method of pruning depend on the type of hydrangea you have, as different varieties have different flowering habits.
These hydrangeas bloom on old wood, which means they form flower buds in late summer or fall for the following year. Pruning them in late winter or early spring before they start to grow new shoots can remove these flower buds and reduce flowering.
If you must prune, do it immediately after flowering (usually in late spring or early summer). This allows the plant to develop new growth and set flower buds for the next year. Remove dead or weak stems and thin out crowded growth to improve air circulation and overall plant health.
Panicle hydrangeas bloom on new wood, which means they form flower buds on the current season's growth. This makes them more forgiving in terms of pruning timing.
Prune them in late winter or early spring before new growth begins. You can cut them back quite hard if needed. Remove dead or weak stems and shape the plant as desired.
Smooth Hydrangeas, i.e. 'Annabelle'
These hydrangeas also bloom on new wood, so prune them in late winter or early spring. You can cut them back to within a few inches of the ground if desired. This encourages robust new growth and larger flowers.
Oakleaf hydrangeas produce their flower buds in early summer on the previous year's growth. So, if you need to prune them, do it right after flowering in late spring.
Remove dead or weak stems and shape the plant as needed.
These hydrangeas can be pruned in late winter or early spring before new growth begins. Prune to control size and shape, removing any dead or tangled growth.
Always use sharp, clean pruning shears or loppers when cutting hydrangeas to make clean cuts and minimize damage to the plant.
Here's a 4-minute video that shows how and when to prune the different kinds of hydrangeas.
Remember to remove any dead or diseased growth regularly throughout the year to maintain plant health.