I bought a red magnolia that was sold as being able to grow on a patio in a pot , so not too high. I have had this one for 4 years and it has not flowered. It is perfectly healthy and is decidious but only produces leaves. It is in proper soil for magnolias.
Certified GKH Gardening Expert
You should fertilize this at least once per year. This is likely the cause if it doesn't get fertilized regularly. I would also add dolomitic lime to keep the pH stable. This can help it along as well.