All Clematis like a deep, cool root run - so a large pot would be best, with other plants in the pot, or possibly a pebble topping, to shade the roots. Don't let the pot stand in a sunny area, or the roots might fry!

thanks for the info. I am planning to use a big pot for C. Josephine so we'll see how it goes. Regards, Frank and Glad

Good luck! :-)