I have heard there are a few varieties of gardenia that are hardy to zone 6. One of them is called Frost Proof. Since gardenias can die very quickly and easily indoors, you might actually be better off trying to push your zone limits a bit and find a warmer micro-climate in your yard where it can overwinter. For example, you could try planting it close to your house's foundation in the warmest part of the yard with lots of mulch, or maybe overwinter it in your garage. If you do try to overwinter it inside, my experience has been that the ideal for them is a combination of: cool temps, high humidity, and lots of light. This post was edited by summersunshine on Fri, May 2, 14 at 20:04

Hhhmmmm...well I don't think anywhere that close to DC actually got below 0F. "Rock Creek Park" officially stops inside the city. At any rate no gardenia is going to truly be zn 6 hardy and obviously the existing so-called hardy ones are only hardy for mild-to-moderate zn 7a conditions. I had both 'Kleim's Hardy' and a smaller 'Chuck Hayes'; considering the CH was much younger it died no more quickly, maybe even a bit less quickly. But by the, what was it, 5 or 6th round of record low temps in early March, they were both dead. Both would have been fine with the first drop to 3F if it had been the only one, and the KH had almost never been injured before. I'll probably just replace at some point w/CH, since the flowers are a little showier and no less fragrant. But they are both still deserving shrubs in the DC area IMHO, dying once every 20 years is manageable for a shrub if you don't mind the replacement cost and aren't using it as a "foundation" shrub. (OMG honey, our house lost its foundations! We'll have to move!) This post was edited by davidrt28 on Tue, May 20, 14 at 5:28

Hines collapsed, supposedly due to gross mismanagement so if you are interested in the Frostproof buy it while you can.

Yeah, well, the picture that emerges is this: when a plant is hardiness rated to zone 7, yes, I'm sure it survived single digit temps. somewhere. But as this winter proved, does that mean it can survive a month of repeated single digit temps, high winds, and extended cold spells below freezing? I noticed the first round of 3F did little damage to my gardenias; each successive cold spell was another blow. Even at the very beginning of March, my 'Chuck Hayes' still had a bit of green, and I wonder if we'd had an almost frost free March like some past ones have been, would it have managed to recover? But, no, we went onto have yet another cold outbreak, hitting single digits _again_. That finished it off. (Baltimore recorded its coldest March morning low in over 140 years of weather records!) I'd had a 'Klein's Hardy' since 2006 that had shown no damage. I think I will wait a year to replant, but I probably will, and I will consider this winter a (hopefully) terrible aberration. So many things were outright killed that had never shown damage since 2005. (Or for certain plants I'd grown since the mid 90s, for 20 years. For example I'd never seen a winter damage Erica arborea alpina at all around here; this winter killed 2 of mine. In that case, it was because the heavy snows and winds combined with the freezes to rip their trunks apart) This post was edited by davidrt28 on Wed, Apr 30, 14 at 14:55