You can start magnolias from seed, from stem cuttings, by several methods of grafting or by air layering. All methods of propagating magnolias have advantages and disadvantages, but the process that gardeners will find most reliable for its level of difficulty is air layering. This process it to cut into the stem of a magnolia plant, then bandage the wounded area by wrapping it in sphagnum moss and keeping the air-layered magnolia constantly moist until the upper portion of the stem produces roots. The rooted section is then potted and, when established, transplanted to the yard or garden.
Select a healthy stem of at least 1/2 inch in diameter on a mature magnolia. Make two cuts around the stem. Each cut should be between 1 and 2 inches long and parallel to each other. Cut through the bark and into the outer layer of the stems. Make a vertical cut connecting the first two cuts. Peel away the bark and the outer layer of the stem, which will expose the inner woody tissue.
Wrap damp sphagnum moss like a bandage around the cut. The moss should be soaked through, but squeeze out excess water before wrapping. Secure moss with string if it does not adhere to stem, but do not wrap not tightly.
Wrap a piece of polythene film carefully around the moss-covered stem. Hold together the ends of the film and fold vertically together until tight (three or four turns). Fasten ends of the film sheet securely with electrician's tape. Make certain that the tape meets the stem beyond the edge of the film on both ends so it adheres. This cover is to hold the moisture inside.
Remove the rooted branch from the top of the plant when the roots are visible on all sides of the moss. This process may take two to three months. Use a sharp knife or shears. Cut just below the moss ball. Remove the polythene film. Do not disturb the roots or remove the moss.
Pot in a good potting soil and place a polythene tent over the pot for a week or less, giving the roots a chance to become established. Keep plant out of strong sunlight.
Gradually expose magnolia to an unsheltered atmosphere by cutting three holes in the polythene covering every few days to let in air from outside.
Plant the magnolia in the yard or in a larger pot as the tree outgrows its container.
Air-layer the magnolia on wood from the previous year if it's done in the spring. Air-layering can also be done midsummer on the most mature shoots from the current season's growth.
Patience during the final stage is very important. Do not rush the new magnolia to set down its roots in the pot.