In article , Charlie
Pridham writes

I know opinions as to pot growing clematis vary ! but I have grown some of
mine in pots for years BUT although I use just 10lt pots, I repot every year
in the same pot (removing about a third of the root ball each time) but the
size difference of both the plant, and the flowers on it are quite marked.
Alternatively some customers pot grow for 2-3 years then plant that plant
out and replace the one in the pot. So long as you accept that in a pot, its
a pot plant, and needs that level of care, everything is fine :~)

Yes. A friend of mine has grown hybrid clematis in pots for years and
years. Even quite tall ones like Ville de Lyon, and they are fine
because she does exactly what you do. And as you say, the alternative
is to treat them as a 'long term 3/4 year bedding plant' & then plant
out in the garden & start again.
--
Rachel
Clematis Web Site
http://www.ukclematis.co.uk/