Gardenias are subtropical plants that thrive in warm, humid weather. Most gardenias are hardy in zones 8-11, though a few varieties hardy to zone 7 have been developed and a few are only hardy in zones 10 and 11. Gardenias can be grown in pots and brought inside in cold climates. See How To Care For Gardenias for more information.
Several years ago, I bought a little gardenia bush. According to experts, if protected during cold snaps for the first few years, mature gardenias can survive an occasional frost.