It is one of the more cold hardy cultivars, though you will still want to keep it in a protected location. From my experience, 6 degrees in a protected location still caused some tip dieback.

I've never heard hardy gardenis referred to as "frost proof." See the link below.

Here is a link that might be useful: Hardy gardenias

It's a cultivar, just like 'Kleim's Hardy', 'Griff's Select', and 'Chuck Hayes'. Search the internet. It's one of the more popular cold-hardy types.

I bougth 'frost proof' gardenia last year and planted it next my deck. last week I went to check on it and the plant is good with lots of greenleaves. I am glad that it survived extreme weather conditions and 2 major snow stroms this season. I would definitely recommend this to folks in Northern Virginia. It bloomed continuously last summer, I will look to buy some more this year. As far as chuck hayes goes, the stems are green with few greenary but most are crisp brown leaves, will check later on this month to see if that survives. 'Frost proof' gardenia is the best for fragrant plant lovers who love growing gardenias.