Common Name: Thunberg's gardenia
Type: Broadleaf evergreen
Family: Rubiaceae
Native Range: Southern and eastern Africa
Zone: 10 to 12
Height: 6.00 to 15.00 feet
Spread: 4.00 to 10.00 feet
Bloom Time: Seasonal bloomer
Bloom Description: Creamy white
Sun: Part shade
Water: Medium
Maintenance: High
Flower: Showy, Fragrant
Leaf: Evergreen
Other: Winter Interest
Culture
Winter hardy to USDA Zones 10-12 where it may be grown in the garden in humusy, organically rich, acidic, well-drained soils in part shade. Consider raised plantings in areas with heavy clay soil. Water plant soils consistently. Plants appreciate significant humidity year-round. In the St. Louis area, plants should be grown in pots or containers in greenhouses, conservatories or warm rooms. Plants may be taken outside in summer, but should be brought indoors in late summer/early fall for overwintering. As an indoor plant, grow this gardenia in bright light with moderate room temperatures. Water moderately, but do not allow soils to dry out. Prune as needed after flowering to shape. Fertilize as needed from March to August. Gardenias need lots of attention and are generally considered to be difficult plants to grow well.
Noteworthy Characteristics
Native to South Africa, Gardenia thunbergii, commonly called white gardenia, is a tropical/semi-tropical evergreen shrub that typically grows to 6-15’ tall (smaller in containers) and features glossy, elliptic to oval, conspicuously veined, green leaves and solitary, extremely fragrant, showy, mid- to late winter flowers. Each flower (to 2.5” across) is creamy white with a tubular corolla with 8 large spreading petal-like lobes.
Genus name honors Alexander Garden (1730-1791), Scottish physician, botanist and zoologist who settled in Charleston, South Carolina in 1752.
Specific epithet honors Carl Thunberg (1743-1828), botanist, naturalist and pupil/friend of Linnaeus.
Problems
Watch for scale, white flies, aphids, mealybugs, thrips and spider mites. Powdery mildew, leaf spots, dieback, anthracnose, sooty mold and canker may occur. Leaves may yellow (chlorosis) if plant soils lose acidity. Buds may fall and/or leaf tips may blacken if temperatures or soil moisture fluctuate too much.
Uses
In St. Louis, this gardenia is planted in large containers as a greenhouse plant or houseplant that may be taken outdoors in warm growing season months.