unless there is some kind of safety problem or

unless you are trying to control Annabelle-like blooming problems (heavy blooms flatten out the stems) then

hydrangeas do not need to be pruned. If you find that you need to prune an unknown hydrangea, do it after it blooms but before the months of August-September.

About the bloom problems.... your hydrangea may be planted out of zone and needs winter protection techniques applied in order to successfully bloom. Lack of these allow the winter drying winds to either kill the flower buds, the stems or both. Hydrangeas that regularly grow from the ground every year in Spring are the perfect example of this. The stems have dried out killing the stem and its flower buds.

But hydrangeas that grow just one zone less than their maximum zone can leaf out from old stems whose flower buds were killed by winter. Nice if you like the green leaves but frustrating if you want some bloomage now and then.

So what do you do? Well, apply these winter protection techniques. There are two methods discussed in the forum. One covers the plant with a cardboard and then with leaves on top. The other uses a wire mesh cage around the plant that gets covered with leaves to help insulate the plant's stems. Have you ever applied winter protection to hydrangeas? If not, check out this link by hayseedman. It is very good and has lots of pictures.

Most hydrangea macrophyllas have blooming problems as one goes further and further north so it is very likely that this is the type that you have. If you have colored blooms at blooming time then you probably have one of these (of course, some macrophyllas bloom white so whites are more difficult to differentiate from other hydrangea varieties). Oakleafs should be hardy in Zone 5 and paniculatas/arborescens can be hardy in even colder zones.

Does this help, claga?
Luis