Glossy green leaves with fragrant white, tubular flowers are the hallmark of tropical gardenias. Although more than 60 species of gardenias are known, fewer than 10 are commonly grown in gardens that never receive frost. Moist, well-draining soils that in general are not alkaline in pH allow tropical gardenias to grow their finest and present amazing floral displays.
Randa (Gardenia carinata) is native from India to Malaysia with glossy, deep green evergreen leaves, reaching a mature height of nearly 40 feet. The intensely fragrant flowers have five petals on a slender tube. They open ivory white and age to beige and finally buttery yellow. Easily grown from seeds, this species needs a sunny location in a frost-free climate, USDA Zones 10 and warmer, and a rich, deep, acidic soil that has lots of moisture and organic matter.
Also native to Southeast Asia is the orange gardenia (Gardenia coronaria). This evergreen shrub, maturing to a height of 10 to 15 feet, has glossy green leaves that are slightly undulating on their margins. In the warm months, trumpet-shaped flowers emit a slight pleasant fragrance. They first open off-white and quickly turn yellow-orange in color. Grow in USDA Zones 10 and warmer in a moist, well-draining soil that is not alkaline in full or partial sun exposures.
Amazing with large white flowers that are up to 10 inches in length, the shining gardenia (Gardenia imperialis) hails from the jungles of Sub-Saharan Africa. It is a large tree native to wetlands with large leaves that are amazingly glossy. Grow it in USDA Zones 10 and warmer in wet soil that is rich in organic matter and not alkaline. Full sun exposures are best.
In equatorial lowlands in Malaysia and Borneo grows the water gardenia (Gardenia tubifera). Reaching nearly 60 feet in height, its bark is ghostly gray and smooth, while twigs are pale yellow. The fragrant white flowers turn orange with age. Growing requirements match those of the shining gardenia.
From tropical eastern Africa comes mukumuti (Gardenia posoquerioides). It is a rounded shrub, reaching 20 feet with great age. The leathery leaves whorl around the branch tips from where the eight-petaled white flowers are borne. Grow in partial to full sun in a moist, humus-rich soil that is not alkaline, USDA Zones 10 and warmer.
More tolerant of frost in winter, the Natal gardenia (Gardenia cornuta) is a shrub or small tree from the thickets of South Africa. The shiny green leaves are clustered in whorls of three. The long-tubed white flowers are fragrant and turn deep cream when old. The yellow fruits are eaten by monkeys in the wild. This species needs growing conditions similar to orange gardenia, but will thrive in USDA Zones 9 and warmer.
Synonymous with the South Pacific island of Tahiti, tiare (Gardenia taitensis) is also called the Tahitian gardenia. The white flowers are intensely fragrant and often used in leis and head garlands. The tongue-like glossy leaves are shiny and hide the smooth gray branches. Native to coastal lowlands of the southwestern Pacific islands, it is tolerant of seaside conditions and slightly alkaline soils, but ideally the soil should be moist, sandy, rich in organic matter and acidic. Grow in USDA Zones 10 and warmer.
Found naturally only in South Africa as a small tree that grows to 15 feet in height, white gardenia (Gardenia thunbergia) blooms from winter to spring. The solitary flowers occur on the tips of branches where clusters of the glossy green leaves grow. Blossoms have many overlapping white petals and turn creamy beige as they age. Tolerant of light winter frosts, culture for this species mirrors that of Natal gardenia.