Bachelor's Button, Japanese rose, Jew's Mallow, Japanese Kerria
Kerria japonica
Family: Rosaceae
What it is like
Bloom Color: Yellow. Main Bloom Time: Early spring, Late spring, Mid spring . Form: Spreading or horizontal, Upright or erect, Weeping.
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.
Height (m): 2
Where it is found
By rivers and on rocks in gorges in the mountains. Thickets on mountain slopes at elevations of 200 - 3000 metres.
E. Asia - China, Japan. A rare garden escape in Britain.
Conservation Status:
Countries/locations it is found in
How it is used
Food
Rating: 1
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.
Medicine
Rating: 1
A decoction of the flowering shoots is used in the treatment of coughs and women's complaints.
Vitamin C: Plants good for their vitamin C content
Women's complaints: A very vague title, it deals with a miscellany of problems peculiar to the female sex.
Other
Rating:
How it is grown
Landscape Uses:Container, Foundation, Pest tolerant, Massing, Specimen. 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. Special Features: Not North American native, Attractive flowers or blooms.
Propagating it: 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.
Best place to grow: Woodland Garden Dappled Shade; Shady Edge;
Habit: Shrub
Hardiness: 4-9
Growth: Medium
Soil: Light (sandy), medium, heavy (clay)
Shade: Semi-shade, no shade
Moisture: Moist
Things to keep in mind
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.