Whether the vine flowers on old or new wood really has no bearing on its hardiness. Most pruning group 2 vines - the bulk of the large flowered hybrids (including your 'Proteus') - bloom at least in part on old wood. And cultivars of C. florida are included in pruning group 3 - those vines that bloom on new growth.

However, Clematis florida has a reputation of being a somewhat difficult clematis to grow. Most literature suggests it is only reliable to zone 7(6) and placement in a protected location and a lot of English sources indicate best placement is in a conservatory or greenhouse in winter. I've tried this vine several times without success and I've grown a lot of different clems in my day....even my zone 8 garden is not a guarantee to winter this vine over.

I would take any zone ratings for clematis, especially if they come from observations made by the British, with a grain of salt since their winters can be quite different than ours here in most parts of the US. The exact hardiness ratings of most clematis are not known with any certainty and their hardiness ratings may vary within any given gardening zone based on the winter conditions (say a zone 6 where it stays cold most of the winter vs. a zone 6 where the temperatures vacillate over the course of the winter). COTW is performing a survey to get the hardiness ratings/survivability of clematis from gardening zones around the world to help put some more data together on this subject.

Clematis florida 'Sieboldii' is grown by friends in Michigan with no problems and the Toomey and Leeds book says it can be hardy to zone 6. Here in my zone 7a garden I had it survive winters quite nicely but the main problem with it was that it wilted several years in a row right as it was starting to bloom so it was removed from its place in the garden.

Clematis florida 'Plena' is a sport of C. florida 'Sieboldii' and the Toomey and Leeds book says it is hardy in zones 7-9. Whether is would survive in your Michigan garden is uncertain but the only sure way to know for certain is to try it and see how it goes.

There does seem to be confusion out there about the pruning types that C. florida the species and any of its cultivars fall into since Toomey and Leeds Encyclopedia lists the species as a type 2 and COTW lists it as a type 3, the Toomey and Leeds book says that Sieboldii can be treated as a type 2 or 3 and COTW lists it as a type 3, and the Toomey and Leeds book lists florida Plena as a type 2 and COTW has it is a type 3.

Bottom line is that regardless of the pruning group a clematis may fall into, the hardiness ratings are not know with certainty, the only way to know if it will survive in your garden is to try it, and the fun in gardening is finding out what works and doesn't in your own individual microclimate.

I know that I have listed this before but the owner of Seneca Hills Perennials, Ellen Hornig, sums it up best about using the gardening zones ratings as an indication of whether a plant will survive and flourish in your garden or not. See the link below and the section entitled Plant Hardiness concerning this.

Here is a link that might be useful: Take on Plant Hardiness Ratings

Whether or not it is an issue of hardiness, Clematis florida is not the easiest of clematis vines to grow. It is certainly not one I'd suggest for someone new to these plants.

For a number of years, I have been receiving plant evaluations based on field trials conducted by the Chicago Botanic Garden. I don't always agree with their conclusions - they are intended primarily for upper midwest gardeners - but it is interesting information to review nonetheless. The trials are not just based on hardiness but on ease of growth, flower production, susceptibility to pests and diseases and general garden performance. Obviously, the conclusions might be quite different if the same plants were trialed elsewhere. The Pacific Northwest does have a similar evaluation process, Great Plant Picks, and again, it is directed towards PNW growing conditions.

This clematis evaluation is not too recent and it only brushes the surface of possible cultivars but it could be helpful for those located in the immediate area and are new to growing clematis.

Here is a link that might be useful: CBG clematis evaluations

GG, the person was asking about Clematis florida 'Plena'
and not the straight species Clematis florida. I don't think you can lump the species and hybrids derived from any species into the same basket as to how easy they are to grow. What the species is crossed with can have a large influence on how hardy the resulting hybrid is.

Irrespective of this, I saw in a post on the Trees forum that you can't get brugmansias to survive in the ground in your zone 8 whereas they do survive for me and others in my zone 7a/7b. This only goes to show that what is difficult to grow in one zone may be much easier to grow in another lower numbered zone. Sometimes it has to do with things other than the hardiness rating and a particular zone. I am of the ilk that it is better to try and fail and at least know that something won't grow for you than to just assume it won't and never try. There have been numerous postings on this forum over the years about how variable the vigorousness of many different specific clematis are in various gardens. As I and others on this forum have found, clematis don't read books and often perform in an individual's garden in ways different than how they are supposed to.

Gee, thanks Miguel for the complete dressing down! I'm not sure if you meant to be as condescending as both your posts read to me but it came across loud and clear. I can ignore one but two in a row is a bit much.

FWIW, I am not the only one that has had diffculty with this particular species (and 'Plena' is only a named form of the species - technically a varietal that has been assigned cultivar status). Searches under this name very often come up with admonitions of the need to site it in a "sheltered" location or that it poses some challenges in growing that are not usually encountered with other clematis. And while I have no intention of discouraging anyone of experimenting, I see nothing wrong in letting them know they may encounter less than ideal results, especially if they are new to growing clematis.

btw, winters in the UK tend towards the mild compared with much of the US as their climate zones compare with our zones 7a to 10a. If it's tricky to grow there, it's hard to imagine it would significantly easier here or in colder zones.

Not to be a dressing down but an explanation of my position on the specific clematis the poster asked about. I am not saying that you haven't had issues with the "florida" clematis but that there are lots of clematis out there that some people have trouble with and that others don't. The brugmansia reference was just to point out that here is another plant that you have issues surviving in the ground in zone 8 that we can get to grow and survive in a zone colder than you are in. This points out once again that it must be something other than the cold that does it. Perhaps it is more of an issue with people who garden in climates that are wetter or where temps vacillate versus one where it gets cold and stays that way. That may explain why growers in the UK with milder temperatures during the winter than many of us here in the US have issues with clematis surviving their consistently wet and milder temps outside than we do. Like I said in my first post, I know of people in Michigan and Chicago who grow one of the florida cultivars and they are perfectly hardy there but they won't grow in your zone. There have even been people in zones 6 and 5 who grow montanas quite successfully and actually get them to bloom although it is often said that trying to grow them there is not worth the effort. Enough said about this issue on my part.

B, IMHO, and in answer to your question, I wouldnt bother. There are other choices of clems or vines to grow that will give you more pleasure than having to baby an unhappy plant. If the green idea is one you want in a flower, perhaps try Alba Luxurians Viticella, I havent grown it, but it has green touches on the flowers in the spring. According to Silver Star Vinery, it is hardy to a zone 3.
Kat

I live in Michigan and I, in my yard, have both Florida "sieboldii" and "flore pleno" in the ground. I'll be as honest as I can.

I have grown each for about 3-5 years. "fp" was a weaker grower for me right from the beginning. It might have just been a younger plant than I generally purchase, but I wasn't impressed the first year, though it did produce one small flower. "s" has been a better grower for me. Niether plant is in a particularily good area, I just kind of squeezed them in where I could.

Each one has gone underground for at least 1 summer that I have had them. (in other words they've either not returned, but did the next year or they were so tiny and unimpressive that I didn't even notice them during those summers)

"fp" did impress me this last year and I actually didn't hate the flower this last year (its 4th I believe) **It was a mail order mistake that my wife fell in love with**

If I were you, I'd consider either of them, and if I grew it, I'd try to keep it close to the house foundation. If you were a good friend of mine (and lets imagine that you are :) then I would tell you to also (or instead) consider Passiflora Incarnata. Its an equally striking vine that doesn't have hardiness problems of any sort related to them in zone 5. Its also a much easier plant to grow.

In my own defense here, I grow more than 20 clematis on my little 1/8th acre and in the right spot and when well grown they are frequently just the right plant, but in this case (with the poster's concerns) I just think it might not be the best choice.

It does look great when paired with "fp" p. incarnata and Asao when in bloom though.

~Chills

Thank you all for your insight and the lively debate! My only sheltered spot is on the west side if the house near the foundation-it would only get late afternoon/evening sun.
So as much as I admire that frothy lime sorbet color, it would be in my best interest to find something not so fickle for my zone 5!
-B

Let me chime in as well - though I do grow C. florida, it just doesn't do all that well compared to the ones I grow in pots and keep in a cold basement during the winter. The ones in the ground bloom some, but are hardly worth it, I think. In pots = wow! They are hardy, but struggle after most winters here.

Proteus will also be sketchy for you, because of some of its heritage as well, and similarly-colored Comtesse du Buchaud will do much better. After a mild winter, though, Proteus' double blooms are just amazing.

FWIW, gardengal, the Chicago Botanic Garden clematis trials don't seem to all that accurate to me, either, and I live just a few miles from them. Some that they say don't perform well do spectacularly for me.