Rhamnus japonica aka Japanese Buckthorn

Rhamnus japonica, or Japanese buckthorn, belongs to the Rhamnaceae family. This deciduous plant grows in the temperate parts of Japan. Kew lists its native range as Hokkaido and western Honshu. Plants For A Future gives a wider range across Japan. Its list also includes Kyushu and Shikoku. These sources differ on the extent of its native range.

In gardens, Japanese buckthorn forms a shrub about 10 feet [3 metres] tall. Kew also records its growth form as a tree. It loses its leaves during the year. Plants For A Future notes that its form can vary. The species flowers in May, and insects pollinate its blooms. Each flower has both male and female organs. The supplied species records give no flower colour or fruit description. They also give no mature spread or detailed leaf description.

This shrub can grow in sun or partial shade. Plants For A Future places it along woodland edges and in dappled shade. It prefers moist soil and accepts a broad range of soil textures. These include sand, loam and clay. It also grows in mildly acid, neutral or mildly alkaline soil. The same source lists USDA hardiness zones 4–8. Its modest height suits woodland garden settings where space allows. The evidence gives no species-specific account of pests or diseases.

Plants For A Future lists the leaves as edible, but urges caution. It provides no details on how to prepare them. It reports no confirmed toxicity specific to this species. However, it warns of possible mild poisoning within the genus. This leaves the safety of eating this plant uncertain. Reported medicinal uses include treating fever and skin complaints. The fruit and bark can cause vomiting and act as laxatives. Branches yield a green dye. The close-grained wood has been used to make furniture.

Seed, cuttings and layering offer ways to raise new plants. Plants For A Future recommends sowing fresh seed in autumn under a cold frame. Stored seed needs one to two months of cold treatment before sowing. Young plants spend their first winter under cover. They can go outside the next late spring or early summer. Half-ripe cuttings can be taken in July or August. Mature wood cuttings can be taken in autumn. Early spring is the listed time for layering.