I tend to agree with Dave. I am not sure I believe that any gardenias are really fully hardy
in zone 7a, long term. I've tried "Kleims Hardy" and "Frostproof" and both went into eventual decline. My "Kleims" still seems to regrow slightly from the roots but it's not a satisfactory "shrub" by any means.
Some of you may remember my "Grif's Select". It did great for several years - eventually growing 4+ feet high and wide.
But last winter killed into the ground. It eventually re-sprouted last summer but that little bit of growth got killed with the first days of cold weather in December so I am thinking it may be dead now or will just sputter along, clinging to life before it succumbs.
I'm wondering now if all these "hardy gardenias" were found growing in Zone 7b and survived
some Zone 7a or 6b winters and got "rated" for them - but they never had to put up with Zone 7a / Zone 6b on a regular
basis? So I am a bit of a skeptic on "hardy gardenias" surviving long-term in Zones colder than 7b. Or, maybe, their survival may have less to do with extreme low temps and more to do with day-to-day winter average temps (for example, maybe they just don't handle being frozen repeatedly, over a long winter, and so do better in NC and south, where the average
daily temps are higher, even if occasional lows are in the Zone 7 range?).
One thing I have noticed about Gardenias. They can appear to be alive in spring sometimes, still somewhat green and flexible, but they still sputter out in the end. So I wouldn't pronounce them "hardy", if they still look greenish in April. Better to wait until July / August and see what's left and actually growing!