Scottish's Garden

Wisteria frutescens is a tough, hardy plant, that is usually pretty easy to bring into bloom. On the other hand, it does like good drainage! If you can't find another spot for it, or correct the drainage problem, a pot may be your only alternative. It will need a large pot--at least 70 cm tall and wide--and a sturdy trellis, or wrought iron "umbrella", to climb on. Keep it well watered during the summer, and feed it regularly with any balanced plant food. It may also be a good idea to wrap the tub in bubble wrap in the winter, to keep the soil from freezing all the way through.
By the way, that one doesn't look like the ones that I have raised--it looks more like a W. sinensis. I hope it came from a good supplier.
That's not strictly true, MG - training advice for wisteria is to allow one, two or three vertical main stems and remove anything else, let it get as tall as you want, then cut the top out to force lateral growth, so its certainly possible, with rigorous attention, to only have one main stem. I have a friend who grew one like this in her front garden up a 2 x 2 solid wood post, looked like a weeping tree.
If its got plenty of roots coiled around, repot now into a pot twice the size of that one, using some John Innes No. 1 and multi purpose (really, you need JI No. 2 or 3, No. 1's for seeds and cuttings). Keep checking as the season progresses - once it starts growing you might find it needs potting on again before autumn. If you're not growing it up a support on, say, a fence or wall, then you'll need a large, solid stake of the height you want the plant to be - the problem with that is, how are you doing to fix it in a container, specially while you're still moving it up in sizes, dunno what the answer is to that one. You've got a bit of a problem with training too, because the main stem is short and doesn't look as if its going to grow from the top any more, so select one of the new shoots to become the central one and remove all others till that shoot has thickened up and got to the height you want, then cut it. You can remove small buds and shoots off the stem by rubbing them out before they open, and clipping off larger ones right where they emerge from the woody part. Because you're starting with a short plant, it's going to take longer to train I'm afraid.