Sophora japonica Seeds | Radix Sophorae Kosam Kujin
LATIN NAME: Sophora japonica
COMMON NAME: Sophora Root, Ku Jin, Huai Jiao
Plant Profile
Sophora is a deciduous tree, 10-20 m in the ground, with pinnate leaves, creamy-white pea flowers in late summer and long strings of constricted pods that hang through winter. The flower buds, known as huai mi, are the medicinal part most often sold, and the root bark is also used.
The tree is fast growing and tolerant of poor soil, and it is planted as a street tree and a shade tree in China and Japan. The flowers are heavy with nectar and are one of the best late-summer bee plants in a temperate climate.
Sophora japonica comes from China, Korea and Japan and has been cultivated for so long that its wild origin is uncertain. In Chinese practice the buds are used for bleeding and for what is described as heat in the blood, and the root bark appears in a different set of formulas.
Science & Biotechnology
The flower buds are rich in rutin, a flavonoid glycoside that strengthens capillary walls, and rutin is the compound on which most of the pharmacological work on the species is based. The buds also contain quercetin and isoflavones, and the unopened bud has a higher rutin content than the open flower.
The root bark contains matrine and oxymatrine, alkaloids that have been studied for anti-inflammatory and antiviral activity. Confusion in the trade is common: the herb known as ku shen is normally Sophora flavescens, a different species, and packets labelled sophora root can contain either.
The tree is a legume but it does not nodulate in the way that clovers do, and it relies on mycorrhizal associations. Its tolerance of urban soil and air pollution is why it is so widely planted along streets in East Asia.
Uses & Benefits
The buds are used in Chinese medicine, usually in formulas, and they are also used as a yellow dye for silk and paper. The flowers are a major nectar source for honeybees in late summer, and sophora honey is a recognised varietal in China.
In the garden the tree is grown as a shade tree, a street tree and a bee plant, and its late flowers are valuable when little else is in bloom. Commercially the buds are a traded herb, and the timber is used for small items. The seed is toxic and should not be eaten.
Growing from Seed
Soak the seed in hot water for a few minutes, then leave it in warm water for a day before sowing. Sow 1.5 cm deep at 20-25°C; germination is fast once the coat has been softened.
Plant out in full sun in any well-drained soil. The tree tolerates drought, pollution and poor ground, and it grows quickly when young. Prune in winter to a clear stem if a shade tree is wanted, and remove the pods if seedlings would be a nuisance. The seed is hard-coated and can remain viable in the soil for years. Seedlings transplant well at one year, which is the stage to move them to a final position.
Our Take
A street tree that doubles as a late-summer bee plant and a source of rutin-rich buds, and one that will grow almost anywhere.
Related Reading
Continue exploring with these related plants: