Last winter anyway. I'm always leery when the source for hardiness data for a given plant is the purveyor of said plant. I trust people generally but when there's a vested interest involved....well, it's just better to get your data elsewhere. Ther problem is, of course, that with new plants, there often aren't any sources except the nurseries offering the plant. Anyway Tony, Sean, Dan, et alia are honorable men; look at the description on the Plant Delights website. It almost understates the case. They hint at reports from Zone 6. Well, we aren't in Zone 6 but we threw tiny plans out into bad parts of the open garden last year and as they emerge this spring, it looks like they've been growing underground all winter. Which of course they haven't, but they must have sent out a good network of rhizomes last year that are generating three to four times the number of shoots I remember from last fall. It seems very likely that with careful siting and a bit of coddling they would easily survive a Zone 6 winter or two.They are potentially an exciting deciduous groundcover. Actually, I wonder if they maybe aren't too vigorous. And too hardy. We'll keep a watch on them.
I put a couple small plants into a perennial border last spring but we decided to move them in early summer when they seemed to be a little overwhelmed by the half-days sun they were receiving. Amanda transplanted them into pretty much full shade and they seemed to like it. Their leaves darkened up and they grew at a reasonable rate. We notice though, after a month or so, that apparently a bit of rhizome/root had been left behind and by fall, a substantial colony had redeveloped; by winter, the plantings were essentially the same size. In the fall both groups flowered lightly. The flowers aren't spectacular, but aren't bad for a frost-hardy gesneriad.