Oh dear, boundaryman, I might be a gardening guru, but my maths is appalling - can you tell me the measurements (height, depth, width) of the container rather than the cubic foot one you've got - might as well be swahili to me, lol

Bamboo. That's 2ft x 2ft x 2ft = 8 cu ft

Thanks! According to my Contained Plants book, Magnolia's not a great pot subject, but it doesn't say why - I can't see any reason why Magnolia stellata in particular, for instance, wouldn't be fine in a tub for a few years. The biggest thing is whether the tub is in full sun or shade or a mix - Magnolia generally prefer shadier situations, as does Camellia, another one you might consider. Deciduous flowering shrub/trees to think about would be Syringa (Lilac), Amelanchier, Hibiscus syriacus. Consider also Wisteria - you'd need to put a post in the centre, firmly fixed, and the pruning would need to be rigorous and frequent, but they can be grown in a tub, specially one that size. All these would like a fair bit of sun (other than the Magnolia and Camellia)

Thank you Bamboo,will puruse the garden centre this weekend.

It's occurred to me that they may not mention Magnolia because it loathes root disturbance, and if you want to keep a very large plant in a container for some years, it would eventually need root pruning, so that may be why. But M. stellata is a reasonably small Magnolia anyway.