Magnolia not blooming could be due to our harsh winter. Magnolias form buds over summer for the next spring’s flower cycle. The cold, dry wind over winter can dry out those buds during a rough winter and then there are no flowers. Is your magnolia exposed to a lot of wind? It was a rough winter and I’m hearing about this quite a bit this spring.
A lack of nutrients can also rob the plants of the energy they need to flower. Feed them right away with some Flower-Tone HERE’S A LINK on spring feeding. This won’t help it flower this year but may for next year’s flowers.