Several options exist for propagating a magnolia tree. Although you can grow them from seed, you won't know the color of the flowers until the tree blooms because of genetic changes during fertilization. In some cases, simple cut propagating works, but air layer prorogation tends to give more consistent results.
Select a branch or stem that is at least a pencil width in size. On magnolias, the stem can be much larger.
Make two cuts around the entire stem 1 1/2 inches apart. Cut through the bark and cambium layer.
Make a long cut between the two circular cuts. Peel the bark away to leave the inner wood exposed.
Apply wet sphagnum moss in a ball around the entire wound. Soak the moss for a few hours before use and squeeze out any excess water. Tie the handful of moss in place with string.
Wrap a piece of polyethylene film around the moss. Roll the connecting long edge of the film together to create a good seal.
Reinforce the rolled joint with electrical tape to ensure that it is sealed. Tape the top and bottom edges of the film to the branch with electrical tape to prevent air from drying the moss.
Watch for roots. Wait for the roots to be visible on all sides of the moss.
Cut the newly rooted stem or branch from the plant using a sharp knife or pruning shears.
Remove the film. Be careful not to disturb the moss or roots.
Plant the new plant in a container filled with good potting soil. Thoroughly water the newly potted plant.
Cover the potted plant with a polyethylene tent for 4-8 days to prevent evaporation. This will allow the root structure to develop more fully. Keep the plant in light shade for a couple of weeks, or until the root system is fully developed.
Harden off the new plant by making a series of small cuts in the polyethylene to reduce the humidity of the plant's environment over several days.
Transplant the young plant in the desired location.