Stewartia: Camellia-like Flowers in Early Summer and Brilliant Fall Color

BY CORINNE KENNEDY

Branches & flower buds of a Japanese stewartia at the Tyler Arboretum (photo: Derek Ramsey, Creative Commons-Attribution Share Alike 2.5 Generic License)

After Japanese maples (Acer palmatum species and cultivars), my favorite deciduous trees are those in the genus Stewartia.  Like Japanese maples, they’re small understory trees that are attractive throughout the year.  My own garden has two species, Stewartia pseudocamellia (Japanese stewartia) and Stewartia monadelpha (tall stewartia), as does the Seattle Japanese Garden.  Unfortunately, they’re located along a little-traveled path in the southwest corner of our garden -- and somewhat hidden by other trees and shrubs.  My hope is that someday one of these lovely trees will be planted in a more prominent position.

The genus Stewartia was once widespread around the globe, but is now restricted to two widely separated areas – Asia and eastern North America.  This divergent pattern, resulting from Ice Age climate change, is characteristic of other genera, such as Magnolia and Hamamelis.  Stewartia trees in temperate regions are deciduous, but in tropical areas of Asia some species are evergreen.  Most of the deciduous species are small to medium-sized trees with delicate branching, early summer flowering and attractive fall color.  The genus name, Stewartia (sometimes spelled Stuartia), dates from 1746, nearly a century after Western botanists discovered a member of the genus in Virginia.

My favorite species is the one most widely cultivated -- Stewartia pseudocamellia (Japanese stewartia).   Its Japanese name, natsu tsubaki, means “summer camellia” and refers to the early summer flowers that resemble those of camellias.   Similarly, the second word of its botanical name (i.e., its species name) is pseudocamellia, which means “false-camellia.”  This resemblance is readily understandable:  both Stewartia and Camellia are members of the tea family (Theaceae).

Japanese stewartia is an understory tree native to the mountains of Japan, except for Hokkaido, its northernmost island.  In the wild, it is often seen growing along streams and in forest openings.  As an ornamental, it was planted as a street tree, in parks and near temples.

Japanese stewartia is hardy to USDA Zone 5 (minimum temperature -20 to -10 degrees F), and has no serious pest or disease problems.  It performs best in light to open shade, in rich, acid, well-drained soil high in organic matter.  Here in the Pacific Northwest, its mature size (at 25 years) is about 25 feet tall by 12 feet wide.  Summers here are dry, unlike in Japan, so regular watering is needed.

Japanese stewartia flower (photo: Uleli; Creative Commons-Share Alike 3.0 Unported License)

The 2-3 inch flowers open in early summer from plump round buds.  White, cup-shaped and attractive to bees, they contain a ring of showy golden stamens.  The small blooms open over a period of about 3-4 weeks, rather than all at once, resulting in an extended  display.  Fruits are brownish woody capsules that burst open to release their seeds.

Fall foliage on the new Stewartia pseudocamellia at the north end of the Arboretum’s Azalea Way (photo: Niall Dunne, in the Winter 2018 issue of the WPA Arboretum Bulletin)

Like other hardy stewartias, the leaves of Stewartia pseudocamellia are deciduous, undivided (simple), oval-shaped, finely toothed, and appear alternately on the stems.  In autumn, the medium green foliage changes to brilliant shades of red and orange.  Then, after leaves have fallen, the tree’s elegant branching and attractive bark are more fully revealed.  Trunk and branches of young trees are colored an unremarkable brown, but as the trees mature, their bark peels to reveal patches of pink, tan, gray, cinnamon & plum.  Unfortunately, trees planted in full sun may not develop this lovely patchwork.

Peeling bark on a fairly young Japanese stewartia growing in my garden (photo: Corinne Kennedy)

Stewartia monadelpha is similar to S. pseudocamellia in most respects -- delicate branching, white cup-shaped flowers in early summer, and brilliant red-orange fall color.  Also native to mountainous areas of Japan, it grows well in the same understory conditions as Japanese stewartia but is slightly less hardy – to USDA Zone 6 (minimum temperature -10 to 0 degrees F).  The one-inch flowers are smaller than those of all other species, but established trees are remarkable for their profuse blooming.  The Greek word monadelpha means “with filament or stamens united in one,” and refers to each flower’s central ring of stamens.  There are two common names.  Tall stewartia refers to its growth rate, which is somewhat faster than the rate of other stewartias.  Trees may exceed 60 feet tall in the forests of Japan, but here in the Pacific Northwest a typical mature size (at about 25 years) is 30 feet tall by 15 feet wide.  A second common name, orangebark stewartia, refers to the bright cinnamon-orange bark that develops with time. 

Matured specimen of Stewartia monadelpha with deeper cinnamon-orange bark at the Carl S. English Jr. Botanical Garden, Seattle (photos: Corinne Kennedy)

Both Japanese stewartia and tall stewartia are lovely small trees without serious insect or disease problems.  With upright-narrow habits, they’re especially suitable for small, partly shaded urban gardens.  A single tree makes a beautiful focal point.  Elegant small flowers, brilliant fall color, delicate branching and showy bark make them attractive in all seasons -- and particularly in winter, when the color and architecture of their branching is fully revealed.

Corinne Kennedy is a Garden Guide, regular contributor to the Seattle Japanese Garden blog, and retired garden designer.