Trim a magnolia tree in fall or winter, after it has finished blossoming. Generally, only young trees should be trimmed, as cutting mature trees can cause irreparable damage. You need pruning shears, lopping shears, a hand saw and tree sealer.
Prepare the tools
Before you begin work, disinfect your tools for 20 minutes in hydrogen peroxide. For twigs and small branches, use the pruning shears. For slightly larger branches, use the lopping shears. Cut branches over 1 inch in diameter with a hand saw.
Trim damaged and diseased branches
Any branches that have become broken, dead, decayed or diseased should be removed first. Cut these branches either close to the trunk or close to the intersection of adjoining branches. After cutting larger branches, apply tree sealer to prevent sap from leaking out.
Trim for shape
When trimming a magnolia tree for shape, do not cut multiple branches that are too close together, or there may be gaps when it blossoms. When branches grow upwards, make slanting cuts when trimming. Avoid tearing the bark on the large branches or trunk, as this can damage the plant and encourage disease. Trim cautiously, as severe pruning often causes long-term damage. Though trimming to prevent overgrowth may be necessary, do as little as possible and keep the tree's natural shape in mind.