Growing only 12 to 20 feet tall with lots of low branches, the star magnolia tree (Magnolia stellata) often is regarded as a large shrub with many thin trunks. Rather mundane looking most of the year, this magnolia makes your heart jump, eyes widen and nose perk up in spring when its branches bear many white to palest pink, star-like flowers. Enjoy this plant in the garden in U.S. Department of Agriculture hardiness zones 4b through 9a.
Star magnolia hails from the moist acidic soils of Japan's woodlands. It was introduced into North American horticulture and gardens in the mid-1800s.
Silky, fuzzy gray-brown flower buds don the branch tips across winter and swell in early spring. While temperatures flirt with the freezing point, the buds open to reveal white to barely pink-tinted petals that release a sweet odor and measure up to 5 inches across. A plant in full flower looks like a white-leaved tree or flock of white doves sitting on an oval-shaped plant. After the flowers wane by mid-spring, the medium green oval leaves emerge, first with a faint bronze-green hue. Rarely do fruits form on the tree and endure until midsummer. The leaves drop off in autumn with little yellow or bronzed-gold color change.
Eight cultivated varieties of the star magnolia remain popular choices to grace gardens. Both Waterlily and Centennial bear flowers with excessive and unusual petals, with between 28 to 32 petals in each white blossom. Waterlily's buds are pink, and white flowers are tremendously fragrant. Centennial is the most cold hardy of the star magnolias, surviving at least -30 degrees Fahrenheit and thus the choice for USDA hardiness zone 4, according to American woody plant expert Dr. Michael Dirr. Royal Star is also remarkably cold hardy, white flowering but slower growing than Centennial. Rosea, King Rose and Rubra bear pink blossoms, while Dawn develops white flowers with petals cloaked in a pink stripe.
Plant star magnolia trees in a moist, fertile, well-draining soil that is acidic, although this species is quite tolerant of more neutral to barely alkaline soils (up to pH 7.8) than other magnolias. Situate the plant in full to partial sun locations, not receiving less than six hours of direct sunlight daily. Too little sunlight creates irregularly shaped trees and diminished flowering.
Star magnolia tree roots remain rather shallow in the soil, and are susceptible to drought and soil compaction from lawn equipment. Irrigate magnolias during droughts and consider an organic mulch layer over the root zone to diminish soil compaction and to retain soil moisture and create cooler summer soil temperatures. If you must prune a star magnolia, do it after the leaves appear and in late spring to early summer to diminish the amount of sap bleeding from the pruning wounds. Overall, this magnolia forms a nice shape and should never require annual pruning. Since the flowers open so early in spring, they may be nipped by frosts. Site a plant in a wind-protected location out of low, frost-prone areas.