This is the Hull database's description.
http://www.clematis.hull.ac.uk/clemdetail.cfm?dbkey=2979

Looks like you should follow what the tag says. I'd keep it in a pretty cool spot if you have one by a basement window perhaps. I am notoriously bad with indoor plants and find that the cooler I keep them, the longer they last and the fewer aphids etc. are attracted to them.
You'll probably get more advise from others.

I googled it and came up with the following info:

Clematis Vienetta
Clematis florida var sieboldiana Vienetta

These 4-inch blooms turn green in autumn!

At Last, an EASY-TO-GROW Clematis Sieboldii!
Perfect for containers as well as the garden!

For years Clematis sieboldiana has been grown as a houseplant, but has not been dependable enough for widespread garden use. Well, those days are behind us, thanks to Vienetta! This robust, vigorous, large-flowered variety is suitable for the garden or for your best containers, sporting large, colorful flowers over a long season. And even if you've never gardened before, you can grow Vienetta easily!

The blooms are 4 inches across, with pure white petals that turn chartreuse in the autumn chill. They surround a large, frilly center of black and purple that resembles a Passionflower! And they arise heavily in early to midsummer, continuing all season. Expect 50 or more blooms on a single plant of Vienetta!

This climber reaches just 6 to 8 feet high, making it ideal for container growth as well as the garden soil. It is in Pruning Group 3, and is hardy in zones 6-9.

Since it is supposed to be a hardier form of clematis florida 'Sieboldii', it should make it outside since clematis florida 'Sieboldii' is winter hardy in my zone 7a garden. However, due to how late in the season it is, the conservative approach might be to keep it inside in a cool well lit area and plant it out next spring.

Remembering that Evison is from across the pond, the outdoors over there is not the same as the outdoors here, or in Virginia. Your plant has been in an overheated store and probably greenhouse too. I'd be inclined to keep it very well protected. If you keep it outdoors, it will look dead to your eyes, but it will be OK I think.

I agree with you Marie on keeping it inside this winter since it is so late in the season for me to be planting clematis outside now, as I stated previously. I do think however that it will survive just fine outside here or in Virginia if the plant is planted outside in the spring. For the longest time, Sieboldii was thought to only be hardy in zones 7 and higher and that was according to the British who grew it in conservatories. We all know now that it is much hardier than that with people in zone 5 here in the US having it survive outside. If Viennetta is a hardier form of Sieboldii, then that further reiterates the fact that it should be hardy outside in zone 7a Virginia.

Another thing is that Home Depot usually has their plants outside in a covered area and not inside the store. Not sure if that is the case for carefreeplants' Home Depot or her clematis, but that is where plants are kept in Home Depots in my area. If it has been in such an area, then it may be very well accomadated to the cooler temps. and may even have been exposed to frost by this time of the year.

Thank you both, Marie and Miguel. I really appreciate your posts and advice, which encourages and gives me confidence in growing these amazing plants.

I found the Viennetta so stunning, and I would like to be able to look forward to having it in Spring and onwards. It has about 8 blooms and 12 buds right now.

Yesterday, I went to HD to pick up another one but they were all gone.

Incidentally, I found it among the house plants inside. Actually, another customer had two of them, which I initially thought to be Passion flower. As soon as she put down one, I came down to pick it up and discovered it to be a clematis, which in turn, I immediately purchased.

This is the most unique Clematis I have ever had. I do love all of them, though. :)

Carefree, congrats on your find. I wish our local Home Depots carried some of the more esoteric and newly introducted clematis varieties. All my local stores carry are the more common everyday ones, ones I already have, or ones I don't really care to have. Would love to find some of the neat ones that you and others have found at the big box stores! Good luck with the one you found. Any way we could see a picture of it?

Here are some photos of the C. Viennetta from HD...

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Carefree, what a lovely plant you have there. Thanks for posting a picture of it. I much prefer the pictures I see from someone's garden or collection since some of the professional pictures out there have been doctored up to show the plant off to its best advantage. From your pictures, the Florida heritage in its genetic makeup is very obvious to me. Hope it does well for you!! Now if I can just get my local Home Depots to start carrying beauties like that. LOL

I just received one of these. My mother bought a pot and found two plants in it, so she gave one to me. The label lists is as hardy in zones 4-11.

Leaveswave, I would be very leary of the hardiness ratings listed for any clematis, especially a relatively new one that not much is known about. In the literature, I see most clematis rated as being hardy from zones 4 to 9 and I think that is a generic rating they give most clematis. Some varieties have been found by some to be hardier in zones lower than 4 and others listed as needing warmer zones are being grown in colder climates quite successfully. That is why the survey by COTW is so valuable. They are collecting data on all clematis from people in all growing zones. This information includes hardiness, susceptibility to mildew, wilt, etc. and other factors. Everyone who has not yet contributed their information should do so. In this manner, important and sadly neglected cultural information can be collected on all clematis varieties.

It is so close to Spring and the Clematis Viennetta (Pictured above) that I overwintered has vines that are about 6 feet long.

I am happy that it survived the winter indoors. I am not so sure, though, whether to cut it back when it is ready to be planted outside.

Since somebody mentioned that it is group 3, maybe I should cut it back? My concern is that it didn't go dormant.

I would appreciate your usual helpful suggestions. Thanks in advance.

You should cut it back now just one inch above the axil...Pruning Group 3s bloom on new wood so it won't bloom on any of that old wood from last year....Jeanne

I agree with Jeanne. Cut it back & off the hoop it was originally grown on.

If you look at the base of the plant, carefully, you should be able to see where the last pinch was made. There will be a bit of a stub and then the wrapped branches growing from the nodes above. You should pinch at the set of leaves at least 1/2-3/4 inch above the previous pinch.

After the new shoots break, you should have new flowers in about 11-14 weeks, depending on your weather.

Don't worry about a dormancy period w/ Vienetta. I have one which has blooming pretty much continuously, on my patio, for the last two years.

Best of Luck!!

Thank you both, Jeanne and Gracefull23.

I will cut the plant back. And as soon as the weather permits, I will plant it in the ground.

Anybody still following this threat that might be up to send me a cutting? I desperately want this beautiful clematis but can’t find it anywhere.
-Rachel paxton

Brushwood carries it although they are currently out of stock. But you can be put on a wait list and they will email you when available.

https://www.brushwoodnursery.com/products/clematis-viennetta?variant=34001609486

The last time I asked Brushwood about it they said they were not carrying it. I asked Evison about it and they don't ship to the US. I think it's still patented .

I would like to get a cuttiing of this beautiful clematis . i have been checking with Brushwood for the last 2 years but it always shows out of stock