I think CotW and Evison's website use USDA growing zones.

Maybe it's too early and I haven't had enough sleep, but I don't understand what is so alarming. I checked the average temps in Bulgaria, and everything seems ok for clematis.

http://www.climatetemp.info/bulgaria/

We regularly have -20C, at least for several days. If Evison's statemen is correct - hardy to -10C, I can't grow her in the garden. Even in most of UK people will need a greenhouse. Is it possible the boys at Hull U to say hardy for zone 6 without consulting the breeder?

There are mistakes in the Hull database, but the keepers are very good about making corrections if someone points out an error.

However, considering that the Evison site stated it was "fully hardy to -10c, I take that to mean without protection. Viennetta probably survives zone 6 winters if it's protected with a thick layer of mulch during winter.

Janet, thank you for the answer. You are probably right - Viennetta will need some protection. What I wanted to hear is presonal experience: Yes, she is hardy, overwintered without a problem here in Philadelphia. No, she isn't.

I know you wanted personal experience, but no one else was around and I was bored. lol

Maybe you will hear something later :)

I've had several people I know that say any zone below 7A is pushing it for most Florida's..but some have theirs coming back IF planted in a micro-climate area of their gardens..I sure wish you luck and let us know..I know in my Zone of 8B they truly flourish and enjoy my heat...Jeanne

I have a first hand experience with both Florida sieboldii and Viennetta. Two plants died after their first winter here. The lowest temperature was about -15F. Both of them were well established plants with good roots.
The third plant, Viennetta, was a bare root tiny baby from Park's. I planted it next to the house foundation (about 2'). I did not have high hopes for it considering my negative experience with the first two and its pitiful shape. It returned and bloomed for me last year! This year, it is bigger and with more blooms. I told about this in 'My little miracle' thread, Search is not working on GW now...

{{gwi:240721}}

Thank you for sharing your experience, Alina. Congrats on nursing succesfully the piny baby. I have a sheltered place, will pile up mulch around the roots in the fall, and hope for a mild winter

I've got Florida Sieboldii and Flore Pleno and both have survived 3+ years here in Michigan (well, in my warm, Michigan area). One of my FS did disappear for a year (09) only to return this year, but its in a really shady poor area (and since I have a few I've left it there.

Vienetta, I can't comment upon as I have been trying to get one for 3 years now, with no luck. Sorry

~Chills