Good Morning Char, 

Thank you for contacting the U of M Extension Service. 

Have you noticed any problem with the magnolia at this point? Here is a link to the U of M Extension Yard and Garden website: https://extension.umn.edu/planting-and-growing-guides/protecting-trees-and-shrubs-winter

Here is another link: https://apps.extension.umn.edu/garden/diagnose/plant/deciduous/magnolia/

This link is to "What's wrong with my plant?" for magnolia trees. You can work through the potential problems with your tree. 

Many have had problems with magnolia scale: https://apps.extension.umn.edu/garden/diagnose/insect/trees-shrubs/not-obvious/magnoliascale.html

Good Luck!