well a container has advantages to pots.. as you can convince a plant it's really healthy and has growing room with a smaller conntainer.. as there's room to rither side for the roots to run.. The size is quite dependant on the available moisture.. I've mine on a drip system.. which gives themm water a few times a day... so there's always water .. even if it might dry out in the few hours tilll the net bit..
every time I hear the smallest question asked.. I recall the snapdragon flowers I had on my roof.. the seeds were either blown or carried over to an adjacent building where they might have washed over the side along the brick and was captured by a small fisure in the motar.. there it rooted in the motar and grew for a few years.. I could see it from my garden.. there wasn't a real hole or break in the wall I could see.. but it leafed out and flowered all of the time.. with just ambient moisture and what it could suck out of the motar of the wall..
they are amaising ... so give them all you can.. and thye will try and cooperate .. but do plant them all.. you'll soon see which of them are compatable with the location and care available.. Gordon