Do perennals hibernate during winter

Yes, that is exactly what they do. They store up 'energy' all summer & fall, and then when the amount of daylight & temperature trigger them, all that 'energy' goes down into the roots, and the plant settles in for a long winter's nap. Perennials are 'Hardy' to USDA zones. These zones determine the lowest average temp. that a plant can tolerate over winter. For ex. a plant that is 'Hardy' to Zone 6 can tolerate winter temps. that hit -10 deg F. If you planted a perennial that was hardy to Zone 8 in western PA, it would die in the cold winters we have here.