How to prune hydrangeas when you are not sure what kind they are?

Then hold off on pruning this year other than a light trim to keep its shape. Make note of when and where they bloom. See if these guides help you.

https://www.finegardening.com/article/pruning-hydrangeas

https://www.gardeners.com/how-to/pruning-hydrangeas/8852.html

This year, attach permanent plant markers below/on the main stem of each hydrangea, to assist with future pruning.

Hi Jan,

As a general rule, you can prune hydrangeas after they have bloomed. If you look closely, you should be able to tell whether they are blooming on old or new wood when they do bloom. Look at the branch. If it's bright green, it is most likely a new wood bloomer. If the branch changes to more of a tan/gray color, it is most likely an old wood bloomer. The new wood bloomers can be pruned in the fall before they die down or in the early spring before they start to grow. In late spring new branches will sprout and new buds will form. The old wood bloomers have a bud on the actual branch while this year's bloom is still there. You have to be very careful about pruning those. There is also one called Endless Summer (and maybe others) that will bloom on both old and new wood. That's why it's important to figure out which kind of hydrangea is in your garden. Here's an article with more detail that should help you. Wishing you beautiful flowers in your garden. :)

https://www.finegardening.com/article/pruning-hydrangeas