Just so we can be sure of the plant, the common name Banana Shrub is used for Michelia figo. Is that what you have? Al

Al...yes it is. The only reason I think I want it in a container is so I can take advantage of the fragrance closer to the house.

This will easily grow to eight feet. Pruning to maintain a smaller shrub will result in a reduction of the number of blooms and of course the fragrance. This is one of those plants, like Osmanthus fragrans or lilac that the fragrance seems to be carried on the wind and is more noticeable some distant from the plant. I recently removed two from my garden that I had planted as foundation plants. They grew well and bloomed every year but covered the windows. Back to your inquiry I think at least a twenty inch pot would be needed and with re-potting root pruning would probably be required. Either of tapla's mixes would work well. Garden soil would have a drainage problem in the container. Al