Hi Marianne!
I'm so pleased your clematis is doing well now. It's lovely to hear when advice has been successful. Now you come to mention it the Blue Angel (first picture shown) is growing through my winter jasmine. You'll have to post piccies for me!!!
Hi Moggle!
I think that as a general rule, clematis do ok in pots if they aren't going to grow too big. Up to about 8 ft is reasonable - and you could get away with up to 10ft - but bear in mind they will need something to climb up! You will need good size pots - a minimum of 18 inches deep and 18 inches diameter. Avoid plastic pots because they overheat, ensure the base of the plant is in shade, and the soil should be well drained. Water them regularly and sometimes with tomato feed.
The varieties I have in pots are Silver Moon (the 4th picture shown) and Sunset (planted together, and I've got them in a hanging basket), Madam Julia Correvon (7th picture), and Sieboldii (5th picture). I've recently planted Constance in a pot but can't report on it's success yet! I hope this helps you.