Growth. Magnolias have a very unusual root system in comparison with other trees and shrubs because their roots are mainly unbranched and ropelike. The way that the roots curl as they grow can make magnolia roots prone to girdling if the roots circle close to the tree’s trunk.Magnolia roots are also close to the soil surface, with the majority of them within the top foot of soil.The root system of the magnolia plant is wider spreading than most other trees as well. It extends from the trunk a distance that is equal to about four times the width of the canopy.he way that the roots curl as they grow can make magnolia roots prone to girdling if the roots circle close to the tree’s trunk. Magnolia roots are also close to the soil surface, with the majority of them within the top foot of soil.