Star magnolia tree normally reaches a height of 15 to 20 feet at maturity, with a spread of slightly less than that. The shape of its white flowers gives it both its common name and its scientific name. It blooms in March or April, making it one of the true harbingers of spring.
Planting Zones, Sun and Soil Requirements
Indigenous to Japan, you can grow star magnolia trees in planting zones 4-8. Select a site that is well-drained, has acidic soil, and is located in full sun to partial shade. Plant in a loamy soil enriched with humus.
Uses in Landscaping, Main Selling Point
They are attractive enough to use as specimen trees for the spring, when in bloom. As relatively small trees, they are more likely to be seen in foundation plantings or near patios than their larger counterparts.
Although usually classified as a tree, these Japanese magnolias will sometimes exhibit a tendency to grow as multi-stemmed shrubs (bushes).
If you wish to avoid this look, prune away any suckers so as to train your specimen to assume a tree form. We grow my own star magnolia as a tree, but we have chosen to grow another type, namely, the 'Jane' cultivar, as a shrub. "Chosen" may be a bit too strong a term there, because my decision was influenced by some damage this plant suffered in a storm (when it was crushed by a tree limb, which severely "pruned" it).
Mother Nature thus made the initial decision to treat this plant as a shrub; thereafter, we merely contented ourselves with providing the same treatment.
When and How to Prune Star Magnolia Trees, Other Care Tips
The plant blooms on old wood (that is, last year's growth), so prune it more or less immediately after blossoming to avoid losing next year's flowers. People don't generally prune magnolias much (although M. stellata is sometimes a bit more tolerant of pruning than other members of its genus), but we prune away the lower growth as it emerges on my established star magnolia tree, while letting the rounded, spreading crown become dense.
On the one hand, you don't want strong March winds whipping around the flowers too much, because that will cause them to drop their petals prematurely. But on the other hand, planting them in a sheltered spot with a southern exposure can be a bigger mistake, because if the buds open up too early, they can be damaged by frost. Find a balance that's right for your area.
New growers are sometimes alarmed by the "funny growths" that appear on star magnolia trees in the latter part of the growing season. No need to worry, though: those odd lumps are just the pods in which star magnolia tree seeds are contained.