Star magnolia is one of the hardiest of the magnolias (Fig. 1). It is a small tree or large shrub, 15 feet tall with a 10- to 15-foot spread. Typically branching close to the ground, the multi-stemmed form develops with a dense head of foliage. Star magnolia makes a wonderful patio, lawn specimen, or accent tree. Lower foliage can be removed to show off the trunk and to create more of a tree form. Otherwise, the persistent lower branches and oval to round form lend a "large bush" look to the plant. When planted against a dark background, the branching pattern and light gray trunk will show off nicely, particularly when lighted at night. The leafless winter silhouette looks great shadowed on a wall by a spotlight at night. The white flowers have a slight touch of pink coloration, and are produced in spring before the leaves appear, even on young plants. They are extremely fragrant, unsurpassed by most, if not all other star magnolias. Flowers are usually not as sensitive to cold as saucer magnolia, but they can still be injured if cold weather arrives during flowering.
Scientific name: Magnolia kobus var. stellata 'Centennial'
Pronunciation: mag-NO-lee-ah KOE-bus variety stell-AY-tuh
Common name(s): 'Centennial' star magnolia
Plant type: shrub
USDA hardiness zones: 5 through 8 (Fig. 2)
Planting month for zone 8: year round
Origin: not native to North America
Uses: near a deck or patio
Availability: somewhat available, may have to go out of the region to find the plant
Height: 12 to 20 feet
Spread: 12 to 18 feet
Plant habit: round
Plant density: symmetrical habit with a regular (or smooth) outline and individuals having more or less identical forms
Growth rate: slow
Leaf arrangement: alternate
Leaf type: simple
Leaf margin: entire
Leaf shape: obovate
Leaf venation: pinnate
Leaf type and persistence: deciduous
Leaf blade length: 2 to 4 inches
Leaf color: green
Fall color: yellow
Fall characteristic: not showy
Flower color: white; pink
Flower characteristic: spring flowering
Fruit shape: irregular
Fruit length: 1 to 3 inches
Fruit cover: dry or hard
Fruit color: brown
Fruit characteristic: inconspicuous and not showy
Trunk and Branches
Trunk/bark/branches: not particularly showy; no thorns; typically multi-trunked or clumping stems
Current year stem/twig color: brown
Current year stem/twig thickness: medium
Light requirement: plant grows in part shade/part sun
Soil tolerances: clay; sand; loam; acidic; slightly alkaline
Drought tolerance: moderate
Soil salt tolerances: poor
Plant spacing: 36 to 60 inches
Roots: usually not a problem
Winter interest: plant has winter interest due to unusual form, nice persistent fruits, showy winter trunk, or winter flowers
Outstanding plant: not particularly outstanding
Invasive potential: not known to be invasive
Pest resistance: long-term health usually not affected by pests
Use and Management
Star magnolia is intolerant of root competition or dryness, and plants grow slowly, perhaps one foot per year. Plant in the full sun in a rich, porous and slightly acidic soil. It is reportedly hard to transplant successfully and in the north should be moved balled and burlapped when actively growing. In USDA hardiness zones 7 and 8, transplant in late winter while the plants are still dormant, transplant after the growth flush in the spring, or plant from containers at any time.
There are a few other cultivars: 'Jane Platt'— new, superior type with many pink petals when opening; 'Keiskei'— flowers purplish on the outside; 'Rosea' (pink star magnolia)— pale pink flowers; 'Rubra' (red star magnolia)— purplish flowers, darker than 'Rosea'; 'Waterlily'— pink flower buds, white flowers, flowers larger with narrower petals. The "Little Girl" hybrids have an upright habit and flower later than the species, thus avoiding frost injury in most years. They include 'Ann', 'Betty', 'Jane', 'Judy' 'Randy', 'Ricki,' and 'Susan'.
Pests and Diseases
Basically trouble free although scales of various types may infest twigs and leaves. Magnolia scale is the most common scale and can be one half inch across. Overwintering scales can usually be controlled with horticultural oil.
Tulip poplar weevil (sassafras weevil) feeds as a leaf miner when young and chews holes in the leaves as an adult.
None particularly troublesome. Magnolia may be subject to leaf spots, blights, scabs, and black mildews caused by a large number of fungi or bacteria. Leaf spots rarely require chemical controls. Rake up and dispose of infected leaves.
Canker diseases will kill branches. Cankers on branches can be pruned out. Keep trees healthy with regular fertilization and by watering in dry weather.
Verticillium wilt may cause death of a few branches or may kill the tree. Prune out dead branches and fertilize regularly.