We live in Zone 4, per the USDA climate zone maps. It means that plants suitable for our climate need to be hardy to -40.
Hydrangeas are notoriously impossible to grow here. My Mother-In-Law gave me an "Endless Summer" hydrangea last spring, and I'd like to keep it growing.* To that end, I insulated it for winter last week by staking around the plant, wrapping burlap around the stakes, and filling in around the plant and in the burlap with leaves from the Aspen trees.