Commonly found in areas with a large amount of sunlight, magnolia trees have flowering buds that typically are in shades of pink or white. While the trees have a decorative look, they also can interfere with power lines, sewer lines and other areas of a home or lawn. Cutting down the tree isn't enough because the roots continue to grow, which leaves the problem untreated. To kill a magnolia tree, you must stop the tree from growing.
Trim multiple small branches from the Magnolia tree, as if you were pruning the tree. Coat the exposed areas of the tree with a thick layer of house paint. The paint blocks the tree from obtaining nutrients through these limbs and invites pests.
Dig a 1-foot-wide, 2-foot-deep trench around the base of the tree to expose the Magnolia's roots. Scrape the dirt away from the bottom of the tree with a spade or shovel. Spray or pour herbicide over the roots, adding more herbicide until it pools on the top of the roots. Follow the label directions for dosage specifics.
Drill holes around the base of the tree with an electric drill, placing the holes 2 inches apart and at least 2 inches deep. Fill the holes with rock salt. Place duct tape on top of the holes and wait two weeks for the salt to kill the tree.
Cut directly into the tree, using a hacksaw. Create one line running the entire circumference of the tree. For smaller trees, make a cut 1/2 inch wide. For larger magnolia trees, make the cut up to 2 inches wide. Make a second cut 2 inches down for smaller trees and at least 6 inches down for larger trees. Strip the bark from this area, exposing the inside of the magnolia tree.
Spray 1 to 2 milliliters of herbicide directly onto the exposed areas of the tree, following the guidelines of the manufacturer. This forces the tree to absorb the chemicals through several different sources, which expedites tree death. The tree begins dying from the top while the roots also die off.