Osmanthus – a Classic Evergreen bringing Structure & Fragrance to the Garden
By Corinne Kennedy
The genus Osmanthus is an under-appreciated gem of our Seattle Japanese Garden – and a favorite of mine. Renowned plant explorer Dan Hinkley calls it “an aristocratic and highly refined member of the olive family.” Consisting of about 30 species of evergreen shrubs and small trees, Osmanthus is notable for its attractive foliage and small, usually fragrant, flowers. The genus name derives from the Greek osme (fragrant) and anthos, (flower). Most species are native to woodlands in the temperate areas of Asia, but the genus also includes cultivars (cultivated varieties, sometimes called “garden varieties”), and species native to the Western Hemisphere.
There are several kinds of Osmanthus in our garden, but only one is spring-flowering – Osmanthus x burkwoodii. The most prominent kind here, it’s a cultivar, not a species plant.
Our garden also has several varieties of a fall-blooming species native to Japan (and Taiwan). Osmanthus heterophyllus (formerly O. ilicifolius, known in Japan as hiiragi) grows here in Areas I and O. It has many common names, including Holly Leaf Osmanthus, Holly Tea Olive and False Holly. People often mistake it for a true holly (Ilex), but its spiny leaves are arranged “opposite on the stem” – unlike Ilex, which has alternating leaves. “Heterophyllus” means “having the foliage leaves of more than one form on the same plant or stem.” Although the younger leaves are coarsely spiny, mature leaves are “entire” (simple in form, with smooth margins). Both kinds are thick, waxy in texture, and dark green.
O. heterophyllus blooms in late September and October, with intensely fragrant flowers that are mostly hidden by the foliage. They’re small, white, tubular, 4-lobed, and held in small clusters. Fruiting is uncommon. It grows at a moderate rate to about 8-10 feet in height, with an upright habit when young, spreading wider at maturity. In time, it can become treelike -- to 15 or more feet tall. Hardy to USDA Zone 6 (average winter temperature, -10 to 0 degrees F.), it’s widely planted in Japan -- both pruned as a hedge and as a specimen shrub or tree in a mixed planting, allowed to retain a natural form. It was first mentioned, in the 8th century, in Japan’s oldest surviving historical record, the Kojiki.
Holly Leaf Osmanthus grows in sun or part shade, and prefers moist, fertile, well-drained, acid soil. However, it tolerates drought, stressful urban conditions, and somewhat alkaline soils. Unless plants are stressed, it has no serious pest or disease problems. It’s not problematic here in the Pacific Northwest, but can become invasive in the mid-Atlantic region of the U.S.
There are two variants of O. heterophyllus in our garden. Osmanthus heterophyllus ‘Variegatus’ (Variegated Holly Osmanthus) grows in Areas G, S and M. It has attractive green foliage edged in white. Osmanthus heterophyllus ‘Rotundifolius’ (Round Leaf Holly Osmanthus) grows in Area O. The latter has rounded, blunt-tipped, spineless foliage. Both are slower-growing than the species plant.
Spring-blooming Osmanthus x burkwoodii was produced in an English nursery before 1928. The “x” in its botanical name indicates that it’s a cross – in this case, a cross of O. delavayi with O. decorus -- species native to Yunnan and Western Asia, respectively. Common names include Hybrid Osmanthus and Burkwood Osmanthus. It grows in our garden in Areas C, D, F, G, I, L and S.
O. x burkwoodii is a dense evergreen shrub with small, glossy, dark green, slightly toothed foliage. This gives the plant a more delicate appearance than that of the coarser-leaved O. heterophyllus. Its small, creamy white, 4-lobed flowers appear in March and April. They’re not as intensely fragrant as the latter’s blooms. However, the two plants have similar growth rates, preferred conditions, and tendency not to fruit. Both take well to pruning. O. x burkwoodii is slightly less hardy – to USDA Zone 6b, rather than Zone 6.
Combining beauty and adaptability -- and hardier than O. delavayi, the parent it most resembles -- Burkwood Osmanthus is deservedly popular. It’s widely grown by wholesale nurseries and usually available for retail purchase in spring. Garden writers often recommend fall-blooming Osmanthus shrubs instead because autumn flowering is much less common. For me, however, the early flowers of O. x burkwoodii are more significant. Their delicate fragrance pulls me out of my winter hibernation -- and invites all of us to participate in the garden’s spring awakening.
Corinne Kennedy is a Garden Guide, frequent contributor to the Seattle Japanese Garden blog, and retired garden designer.