If u do, you won't have flowers that year. Prune as needed AFTER they flower.

thank you, and what kind of fertlizer do you use? and sun or shade? that is the greatest picture - great job

Photo isn't mine...but I do love hydrangeas as well...so many different kinds. I fertilize with Miracid(They are acid loving plants) during the 3 growing seasons. Follow directions. Don't overfertilize. Different types likke more sun or more shade. Do a little research & pick the right plant for the spot. It's best to avoid DEEP shade and damaging late afternoon sun. They also take daily watering if you live where it is hot and dry.

Hi Stacey,
I never cut my hydrangeas in the fall, only around mid march, when they have started budding. I live in British Columbia and it's at that period of the year that, normally, there is no longer any danger of frost. If you cut them before and there is some frost, the new buds burn and they don't bloom as much.
Usually, I cut them about one and half to two feet above the ground, depending how tall and old they are. If they are already very bushy, I cut them back two buds above the last group of stems.
For sure it also depends on the kind of hydrangeas I am dealing with. Usually, lacecups or dwarf hydrangeas don't like harsh pruning. Personnally I don't use any fertilizer.
Hope this will help a little.

There are many different species of hydrangea, some bloom from old wood, some bloom from new wood. The old wood species are pruned after bloom and the new wood can be pruned anytime. These look like Nikko Blue which would be new wood. There are many websites that can help you identify your species and help you with feeding as well as pruning.

Hydrangea

You are right Reneegarrett, they are hydrangeas. Three different kinds actually. The purple and the deep blue have bigger heads.

In France, and maybe in Europe, they are called "hortensias"