What are "hardy" Gardenias?

A cold hardy gardenia is a variety bred to withstand extremes of cold in comparison with most varieties of gardenia. This is an important distinction. By the standards of much of the continental United States, there is no such thing as a gardenia that is seriously hardy in cold weather. Only these few varieties can withstand more cold than a tender variety including Chuck Hayes Gardenia, Kleim’s Hardy Gardenia, and Frostproof Gardenia. Those recommended for Zone 7 can survive limited exposure to temperatures as low as 0° F.