Magnolias are quite insensitive to fungi and animal pests. However, they quickly resent a wrong location, unsuitable soil or incorrect care and react by turning the leaves brown.
Causes of brown leaves in magnolias
If your magnolia turns brown leaves, there can be various reasons behind it. If not only the leaves, but also the leaf buds and flowers turn brown, late spring frosts are usually responsible. If there is no such thing as the cause, check the location and/or the condition of the ground. Full sun locations are just as unsuitable for magnolias as a location on a lawn or even underplanting. The soil must be slightly acidic, magnolias prefer pH values between 5.5 and approx. 6.5.
countermeasures
If your magnolia is in the wrong location, you should transplant it. Be sure to enrich the soil with acidic rhododendron soil. If only the current location is depleted, it is best to fertilize the plant with an acidic soil fertilizer (e.g. a rhododendron fertilizer). In the case of late frost damage, on the other hand, there isn't much you can do other than wait.
tips and tricks
Avoid pruning your magnolia. A cut should only be made if there is an infestation of powdery mildew or another fungus.