Stewartia

Attractive blooms and appealing bark ensure year-round interest, says Miranda Kimberley.

S. pseudocamellia Koreana Group AGM - image: Floramedia
S. pseudocamellia Koreana Group AGM - image: Floramedia

Some plants really fulfil the brief of year-round interest. Stewartia is one such genus because as well as producing attractive camellia-like blooms during summer they also have lovely autumn colour and appealing flaking bark.

Stewartia is a small genus of shrubs and trees within the camellia family Theaceae. Most of the species are native to eastern Asia, hailing from countries including China, Japan and Korea. There are also two species native to the south-east of the USA, S. malacodendron Award of Garden Merit (AGM) and S. ovata. Their native habitats are woodlands - they are found in semishady conditions and in soil that is on the acidic side.

They are generally deciduous, though there are a few evergreen species such as S. pteropetiolata (syn. Hartia sinensis). Some botanists argue these evergreen types form a distinct group and have reclassified them as Hartia, though others argue they are still Stewartia. These species tend to be less hardy than others - S. pteropetiolata is only considered suitable for the mildest locations.

They form neat large shrubs or small to medium-sized trees that can be grown as a single-stemmed form, but they are particularly nice grown as a multi-stemmed tree. They produce strong, fresh-green to dark-green foliage with good venation and sometimes serrated edges that turn lovely shades in the autumn. Their flowers are nearly always white or cream and resemble those of camellia, earning the name "false camellia". Plenty are produced during their summer-flowering period. They can have brightly coloured contrasting stamens that stand out.

Stewartia are slow-growing trees that have a feature worth waiting for - their bark, which varies in shades of grey, green and brown. On mature trees the bark begins to flake off and reveals other shades beneath, not unlike certain eucalyptus. It helps to make the already attractive silhouette of a Stewartia against a crisp, wintry sky a lovely sight.

The best known species in the UK is S. pseudocamellia AGM. It can grow up to 20m tall but is a slow grower so will take some time to reach that high. It produces cup-shaped white flowers with numerous orange-yellow anthers for about three weeks in midsummer, develops gorgeous autumn colour and has attractive mottled brown, grey and burnt ochre bark. The Koreana Group is highly desirable because they develop even stronger autumn colour and have larger, more open flowers.

Another nice species in the genus is S. monadelpha, the "tall Stewartia", so known because it has the potential to reach 20m but it seldom does so in cultivation. Its most outstanding feature is its smooth cinnamon brown bark that makes the species striking in the winter landscape. The species with the finest bark is arguably S. sinensis AGM, but sadly this is rarely seen. It was first introduced by Wilson in 1901 and has a lovely reddy-brown flaking bark.

Other species that stand out include S. malacodendron AGM, which produces masses of large, white, cup-shaped flowers with purple-blue stamens; S. rostrata, which has pink-tinged flowers; and S. pteropetiolata, which produces masses of white flowers and has leaves held on short winged petioles.

Taking their native habitat into account, Stewartia prefer a moist, acidic soil in a position of partial shade. They are best regularly mulched to lock in moisture and add organic matter. They do not like being transplanted, so decide on the final position carefully because they are slow growers.

Few Stewartia are robustly hardy, many coping down to -15 degsC but affected by late spring frosts. Some are definitely on the tender side, such as S. malacodendron AGM, which will suffer after frosts - its wood rarely gets enough sun to ripen up. Therefore, err on the side of caution and give them a sheltered spot.

What the specialists say

- Jan van Vechel, sales and advice, Van den Berk, Netherlands

"The real beauty of Stewartia is their beautiful autumn colour and the different colours of the stems, shown off when the bark peels. They are relatively slow growers. Some may have had problems with the long, cold winters over the past few years. To counter this, don't plant them in exposed areas in the landscape. This is more a plant for gardens, parks and other sheltered areas.

"We grow four species. S. monodelpha is a slow-growing tree that develops lovely autumn colour. We grow S. pseudocamellia as a feathered tree. It has a nice trunk and autumn colours but is again slow-growing and takes a long time to develop. The Koreana form, however, is considered a good grower, also producing nice autumn colour, nice bark structure and white flowers with yellow stamens. Another good grower is S. rostrata, which we grow as a multi-stemmed feathered form. It has unusual pink/white flowers with yellow stamens."

- Steve Dance, office manager, Burncoose Nurseries, Cornwall

"Stewartia are a valued addition for any woodland garden. They offer lovely camellia-like flowers and their trunks have attractive bark. Another notable feature is the good autumn colour the leaves develop. Stewartia prefer neutral to acid soil and sun or semi shade. They will need to be sheltered from strong winds.

"Of the species that stand out, S. sinensis offers cup-shaped, scented white flowers. It also develops lovely flaking brown bark. I also like S. pseudocamellia, which in ideal conditions could reach 20m. It flowers really easily and will produce good autumn colour."

In practice

- Anne Boscawen, owner, High Beeches, Sussex

"Stewartia are very attractive small trees, with pretty camellia-like flowers that are attractive to bees in June and July. Most are very attractive during all seasons, with flowers, autumn colour and decorative bark.

"They are useful to provide light shade for smaller rhododendrons. They require acid soil and light shade. S. pseudocamellia is the easiest to grow here and the Koreana Group have larger, more open flowers and brighter autumn colour.

"S. sinensis has the best bark but it is hard to obtain. The plants supplied are usually S. monadelpha. Young plants need care, moist leafy soil and must not dry out or get burnt by the sun. We have so far failed to establish most of the American species, but we keep trying. Also, plants originally classified under Hartia are not hardy here."

Species and varieties

S. malacodendron AGM (H5), or the "silky camellia", is a large deciduous shrub or small tree with ovate leaves that produces white flowers with conspicuous purple stamens in the summer.

S. monadelpha is known as the "tall Stewartia" but in the UK becomes a slender, small branching tree that produces white flowers with spreading petals and violet anthers from mid to late summer. Its leaves are a fresh green in spring/summer, turning shades of orange, red and yellow in autumn. Develops flaking bark when mature. Relatively hardy but requires protection against late spring frosts when young. Height: 4-25m. Spread: 3-8m.

S. ovata, known commonly as the "mountain camellia", is a deciduous shrub or small tree. Its white flowers with numerous white, yellow or purple stamens are produced from early to midsummer. Its leaves turn orange, red or gold in autumn and it has smooth, flaking, greyish-orange bark. Hardy to -20 degsC. Height: 5m.

S. pseudocamellia AGM (H5), or "Japanese Stewartia", is a deciduous tree bearing white flowers with creamy yellow stamens in midsummer. It also has attractive brown and grey flaking bark and dark-green leaves turning orange and red in autumn. Needs acid soil, shelter from cold winds and protection from late frosts, which will kill even quite mature plants. Hardy down to -15 degsC. Height: 10-20m. Spread: 8m.

S. pseudocamellia Koreana Group AGM (H5) is the finest form of the species, bearing larger camellia-like white flowers with yellow anthers in July/August and deep-green leaves that turn even better shades of red, orange and gold in autumn. Beautiful pink to red-brown flaking bark is an ornamental feature on mature plants. Broadly columnar, 5-6m high by 3m in 20 years.

S. pteropetiolata can be a tall tree in its native habitat but likely to become only medium-sized densely branched shrubs in the UK. Has textured, leathery leaves held on shallowly winged petioles, hence the species name. Solitary white flowers are born in abundance between April and May. Best grown in an acidic to neutral, humus-rich soil with adequate drainage in full sun to light shade, out of freezing winds.

S. rostrata, or the "upright Stewartia", is a shrubby tree with an upright habit. Its flowers are pink at first, later fading to near white. Its finely-toothed, dark-green leaves turn orange-red in autumn. Also has shallowly furrowed bark that peels when the tree is mature. Height: 4-8m.

S. serrata is a deciduous shrub or small tree with white flowers in June and July, making it the first Stewartia to come into leaf and flower. It has reddish young shoots and serrate leaves with red petioles, and dainty, bell-shaped pendent flowers. Hardy to -15 degsC. Height: 10m.

S. sinensis AGM (H5) is the "Chinese Stewartia", a rare species first introduced by Wilson in 1901. It produces large, fragrant, cup-shaped flowers along its shoots, has toothed dark-green leaves that turn bright red in the autumn and red-brown bark that flakes. Hardy down to -15 degsC. Height: 4-8m. Spread: 4m.

Thank you to Floramedia, which supplied the images for this article from its photo library www.floramedia-picture-library.com.


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