Kerria japonica - (L.)DC.
(L.)DC.
Bachelor's Button, Japanese rose, Jew's Mallow, Japanese Kerria
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helizada
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jennylynxliu
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GBIF
Description
Kerria japonica is a deciduous Shrub growing to 2 m (6ft) by 2 m (6ft) at a medium rate. See above for USDA hardiness. It is hardy to UK zone 4. It is in flower from April to May. The species is monoecious (individual flowers are either male or female, but both sexes can be found on the same plant) and is pollinated by Insects. Suitable for: light (sandy), medium (loamy) and heavy (clay) soils, prefers well-drained soil and can grow in heavy clay and nutritionally poor soils. Suitable pH: mildly acid, neutral and basic (mildly alkaline) soils. It can grow in semi-shade (light woodland) or no shade. It prefers moist soil.
Edible Uses
Young leaves - cooked. The leaves contain a small amount (0.002%) of hydrogen cyanide and are also a rich source of vitamin C (200mg per 100g). Some caution is advised, see the notes above on toxicity. Fruit. No more details are given, but this report is somewhat suspect, the plant does not produce a fleshy fruit and the seed case certainly does not look edible. The fruit is a dry, somewhat plump achene about 5mm in diameter.
Medicinal Uses
Vitamin C Women's complaintsA decoction of the flowering shoots is used in the treatment of coughs and women's complaints.
Known Hazards
The leaves contain small quantities of hydrogen cyanide (prussic acid). In small quantities, hydrogen cyanide has been shown to stimulate respiration and improve digestion, it is also claimed to be of benefit in the treatment of cancer. In excess, however, it can cause respiratory failure and even death.
Distribution
E. Asia - China, Japan. A rare garden escape in Britain.
Where It Grows
TEMPERATE ASIA: China (Anhui Sheng, Fujian Sheng, Gansu Sheng, Guizhou Sheng, Henan Sheng, Hubei Sheng, Hunan Sheng, Jiangsu Sheng, Jiangxi Sheng, Shaanxi Sheng, Shandong Sheng, Sichuan Sheng, Yunnan Sheng, Zhejiang Sheng), Japan (Hokkaidô, Honshu, Kyushu, Shikoku)
Cultivation
Succeeds in most aspects in any good loamy soil. Succeeds in very poor soils. Grows well in heavy clay soils. Prefers a moist well-drained soil in a sunny position with shade from the midday sun. Hardy to about -20°c. Plants are moderately fast growing. They sucker freely and can be invasive. Some named forms have been developed for their ornamental value. This species is notably resistant to honey fungus. The flowers are said to be usually unisexual but we do not know if the plants are dioecious or monoecious.
Propagation
Seed - we have no details on this species but suggest sowing the seed as soon as it is ripe in a cold frame. Sow stored seed as soon as possible in a cold frame, it is likely to require a period of cold stratification. When they are large enough to handle, prick the seedlings out into individual pots and grow them on in the cold frame for their first winter. Plant them out into their permanent positions in late spring or early summer, after the last expected frosts. Division of suckers, removed with care from established plants during the dormant season. Larger clumps can be replanted direct into their permanent positions, though it is best to pot up smaller clumps and grow them on in a cold frame until they are rooting well. Plant them out in the spring. Cuttings of young shoots. Young basal shoots in early summer work quite well. Harvest the shoots when they are about 10 - 15cm long with plenty of underground stem. Pot them up into individual pots and keep them in light shade in a cold frame or greenhouse until they are rooting well. Plant them out in the summer. Layering.
