Should I move this Magnolia grandiflora to a bigger container?

This is a Magnolia grandiflora in a 50L pot - it’s about 8 feet tall and it’s very happy. I have three of them and they’re all happy.



My question is this: what do I do to make sure it stays happy? Do I repot into a bigger container? (A big job but I guess with help I could do it.) Should I root prune it by removing the roots at the edge of the pot with a saw? (That’s what I do with containerised Phillostachys vivax - so far successfully, but that’s in a much larger container.) Or what?

Or should I do nothing other than feed and water until it shows signs of distress? Or is it already too late once it starts to yellow (it’s too late with containerised junipers, Juniperus comminis ‘compressa’ - they can look happy and then suddenly start to die and I’ve learned that there’s nothing you can do to stop it.)

You see Magnolia grandiflora as container street trees in the City - that’s what gave me the idea to try it. I bought this plant about 4 years ago from eBay, it was about 30cm tall when it came. They clearly enjoy container life!

 

I like these but must admit I didn't think they would do well in a pot, yours looks really healthy.
Has it flowered?
TBH, I cant answer your question but would have thought that ultimately it will need to go in the ground, not sure how they would like being root pruned, but eventually a bigger and bigger pot is going to be needed, I would have thought.

 

Hi I cannot see whats wrong with it seems quite happy personally I would leave it

 

That's what I was hoping to hear!

 

Yes it has flowered its head off!

 

There are quite substantial trees in the famous Roof Gardens in Kensington -- I remember once seeing an interview with a gardener there who talked about how these things can grow in shallow soil if they are treated well. Here's a video.

Aerial Filming in London - Kensington Roof Gardens (filmed with a remote controlled hexarotor) - YouTube