When choosing a Magnolia for bonsai, the Star (stellata) species is superior. This slow-growing shrub is bushy and dense, often taking up to 30 years to produce flowers. However, once the flowering begins, you will enjoy white, star-shaped flowers on bare branches that measure about five inches across. The leaves on the Magnolia are large, often measuring up to four inches. The Magnolia can be trained in several styles for bonsai although typically, the informal upright on a single or multiple trunk plant is most common.
You want to keep the Magnolia bonsai in partial shade or full sun but always in a position where it will have protection from the early morning sun, which will fade the colors of the flowers and cause them to die off early. Considered a hardy plant, the Magnolia should be fed about every two weeks when the tree is in leaf. Just make sure a well-balanced fertilizer is used, one low in nitrogen. For pruning, you want to wait until after the Magnolia has flowered. Usually, pruning would take place in midsummer, preparing the plant for the next year’s flowers.
Magnolia should be repotted in the early spring, at the same time flower buds begin to appear. Keep in mind that disturbing the root system of the Magnolia can cause stress to the plant so use caution. The repotting schedule is about every three years at which time just one-quarter to one-third of the rootball should be removed. When repotting your Magnolia, use only bonsai soil mix, something neutral to acidic. Then twice annually, the Magnolia would need an acid-based feed to help neutralize alkaline and/or lime in the soil.
Magnolia can be propagated easily by using air layered or ground methods during the spring. However, you can take root greenwood cuttings in early summer, as well as semi-ripe cuttings in early fall. The best part of the Magnolia is that it is virtually disease free. Things you want to watch for include leaves turning yellow, which would be a sign of too much alkaline in the soil, and aphid insects. In addition, scales, most often during flowering season can be a problem. Simply use an organic herbicide, taking care not to spray while the flowers are open.