Planting Clematis in a Pot

I have been given an ' Arabella ' Clematis. I was thinking of putting it on the patio, which is southwest facing. I looked online for advice and ( like the Hydrangeas ) there is lots of stuff out there but some of it seems conflicting. The Clematis is 38 inches from the top of the pot to the top of the plant and has several flowers on it. What size pot should I be putting it into? I do have a pot, its 18 inches across and 15 inches deep, but I'm wondering if its large enough? It states on a few clematis related web sites that they should be grown in specialist compost. I tried growing one years ago in compost and it wouldn't grow, when it was planted out into the garden it did wonderfully. I cannot remember what compost I used back then, probably general purpose, so maybe that was the problem. So, I'm not sure what is best to use? Some advice would be appreciated please.

 

They like cool, damp, shaded roots, so it isn't always easy to provide that in a pot, especially in weather like this. The pot sounds big enough, though, so you could plant it up, then put it behind a bush with the top sticking out, and put a saucer underneath to catch the drips. It'll probably work.

Never heard of specialist clematis compost - anything with plenty of nourishment and moisture retentive but free-draining (as they love to say on the plant labels) should be OK.

 

I can vouch that it does because that is precisely what I did with the clematis I bought in Feb/March time last year The pots are shielded by laurels and their heads reach for the sun up a trellis. The compost is topped with a generous layer of bark to reduce evaporation of moisture from the soil. The saucers catch enough residual water to give me a fair indication of their H2O needs and ... this year, I began feeding regularly with a fertilizer

A good few years before that, I had clematis (didn't know that is what it was) in a fairly shallow trough which only got the sun late afternoon during the summer. It lasted a good few years then, one year, finally gave up the fight. And it was a real fight for it too: who knew they needed feeding and fresh compost on top every so often - I didn't (shame on me!).

These clematis pots will go with me when I move and next year they will be given a final growing space (when I have assessed the soil/light/shade conditions) of the new house.