Hardy Perennial Plants

That depends on your climate and soil.

From your subject line, I assume you get snow and possibly freezing soil in the winter. If that's true, you will find that perennials for your climate will go dormant in the winter and resprout from the ground in the spring. However, you will still have to protect them from freezing in the winter, possibly by mulching, planting extra deep, or even digging them up after they go dormant and storing them in your basement or garage. This all depends on the plant variety and your climate.