Horticulture/Berberis thunbergii

Berberis thunbergii (Japanese barberry or Thunberg's Barberry) is a species of ../Berberis/, native to Japan and eastern Asia. It is widely grown as an ornamental plant, both in Japan and elsewhere in the temperate Northern Hemisphere. Numerous cultivars have been selected, including plants selected for yellow, dark red to violet, or variegated foliage, erect growth, and dwarf size.

Description
It is a densely branched, deciduous, spiny, suckering shrub which grows 1-2 (3) m high, with a "fountain-like" form when unpruned, though cultivars may be fastigiate to nearly prostrate. It has deeply grooved, brown, spiny branches with a single (occasionally tridentine) spine (actually a highly modified leaf) at each shoot node. The leaves are green to blue-green, very small, spatula to oval shaped, 12–24 mm long and 3–15 mm broad; they are produced in clusters of 2-6 on a dwarf shoot in the axil of each spine. The flowers are pale yellow, 5–8 mm diameter, produced in drooping 1-1.5 cm long umbrella-shaped clusters of 2–5; flowering is from mid spring to early summer. The fruit is a glossy bright red to orange-red, ovoid berry 7–10 mm long and 4–7 mm broad, containing a single seed. They mature during late summer and fall and persist through the winter.

It is sometimes confused with Berberis canadensis (American Barberry), Berberis vulgaris (European Barberry), and other deciduous Berberis species; it is most readily distinguished by the flowers being produced in umbels, not racemes.

Growing Conditions
Well-drained soils in full sun to shade.

Ecology
In recent years it has become an invasive species in parts of the eastern United States; in Canada its cultivation is prohibited as the species can act as a host for ../Puccinia graminis/ (black rust), a rust disease of wheat. Currently there are breeding and selection programs aimed at producing cultivars that are either sterile or produce relatively little seed.

Varieties

 * ‘Argenteo-marginata’: Young foliage with white margins.
 * forma Atropurpurea: foliage purple or red.
 * ‘Atropurpurea-nana’: Foliage purplish red, semidwarf to 60 cm, dense habit, slow growing.
 * ‘Aurea’ Foliage bright yellow when emerging in spring, fading to yellowish green.
 * ‘Bagatelle’: Foliage reddish purple, dwarf to 30 cm.
 * ‘Crimson Pygmy’: see ‘Atropurpurea-nana’, above.
 * ‘Dart’s Red Lady’: Foliage dark purple, fall color red.
 * ‘Erecta’: Truehedge Barberry: Upright form, but not tight with age.
 * ‘Golden Ring’: Foliage purple with yellow margins. Fall color red.
 * ‘Green Ornament’: Foliage purple, upright form, heavy fruit set.
 * ‘Helmond Pillar’: Foliage dark red to purple, fastigiate.
 * ‘Kobold’: Dwarf to 40 cm, dense, heavy fruit set.
 * ‘Little Favorite’: see ‘Atropurpurea-nana’, above.
 * ‘Maximowiczii’: Leaves narrow, green beneath.
 * ‘Minor’: semidwarf, to 60 cm.
 * ‘Pink Queen’: Foliage reddish purple, variegated with pink.
 * ‘Pluriflora’: Corymbs dense, with 5-12 flowers.
 * ‘Red pillar’: Foliage purple, erect form.
 * ‘Rose Glow’: Foliage purple, but emerging leaves variegated with pink.
 * ‘Silver Glow’: Foliaged with mottled white variegation. Semidwarf to 60 cm.
 * ‘Sparkle’: Dense habit, heavy fruit set.

Uses
As specimens, hedges, or barrier plants. The flowers are an excellent nectar source.

Maintenance
Pruning is a rather hazardous undertaking. Fine-pruning is best done in winter, shearing better in spring when clippings can fall into the plant. Branches are somewhat fragile, so care should be taken when raking off clippings.

Readily transplants, but again transplanting is difficult due to the spines.

Propagation
Self-seeds readily. Cultivars propagated by cuttings.

Pests and Diseases
See ../Berberis/ for a list of pests and diseases.