The star magnolia bush is a flowering shrub that grows 15 to 20 feet tall and 10 to 15 feet wide. It is also grown as a small tree. Star magnolia develops several trunks near the soil line, and creates a dense canopy of foliage and flowers. The shrub grows equally well in containers and directly in the earth. Star magnolias are deciduous and lose their foliage during the fall. Flowers appear in the early spring, before the leaves return. Magnolia bushes require very little pruning each year.
Trim the star magnolia in late winter or late summer. Pruning during spring or fall causes the branch wounds to bleed sap. Use sharp gardening shears to make clean, even cuts.
Examine the tree's branches for cankers. Cankers are open wounds on trees that cause weakness and rotting. Left alone, canker disease spreads to other branches on the tree, which eventually leads to tree death.
Use the gardening shears to trim affected branches 3 to 5 inches below the canker wound.
Remove dead branches from the star magnolia bush. Trim spindly, weak branches completely off the bush.
Trim the bush into the desired shape. Star magnolia bushes keep their natural shape and only need to be trimmed to remove dead and diseased branches. To grow the bush in a tree shape, remove all of the branches from the lower portions of the trunks. This creates a tree image, with bare trunks and full canopy.