This becomes quite a large tree so not really suitable for a pot.
This is the RHS advice:
https://www.rhs.org.uk/Plants/95584/Magnolia-liliiflora-Nigra/Details

Agree. You'll need a bath tub just to anchor it properly and who is going to move that where? Even "Little Gem" is too big.

Thank you Sbg & Bg for your advice. My garden is very chalky so I will have to pass on that one. I only wondered as I have a M. Stellata growing in a large pot and it always gives a good account of itself. As they say you can’t win them all. Enjoy your days. :)