Marshpepper knotweed (Polygonum hydropiper)

At a glance

Lifecycle: Annual
Exposure: Full sun

Cultivation

A water plant, growing in shallow water or wet soils. Succeeds in most soils if they are wet and dislikes shade. Smartweed is cultivated for its edible leaves in Japan. Plants seem to be immune to the predations of rabbits.

Propagation

Seed - sow spring in a pot standing in water or in situ. Germination is usually free and easy. When they are large enough to handle, prick the seedlings out into individual pots and plant them out in the summer if they have reached sufficient size. If not, overwinter them in a cold frame and plant them out the following spring after the last expected frosts.

Edible uses

Leaves and stems - raw or cooked. They can also be made into an acid peppery condiment. Seed - raw or cooked. It is rather small and fiddly to utilize. The seed is used as a condiment - a pepper substitute. The sprouted seeds or young seedlings can be used as a garnish or added to salads, they are commonly sold in Japanese markets.

Medicinal uses

Smartweed has a long history of herbal use, both in Eastern and Western herbalism. It is not used very often, and is seen more as a domestic remedy being valued especially for its astringent properties which makes it useful in treating bleeding, skin problems, diarrhoea etc. The leaves are anti-inflammatory, astringent, carminative, diaphoretic, diuretic, emmenagogue, stimulant, stomachic, styptic. The seed is carminative, diuretic and stimulant. The whole plant, either on its own or mixed with other herbs, is decocted and used in the treatment of a wide range of ailments including diarrhoea, dyspepsia, itching skin, excessive menstrual bleeding and haemorrhoids. A homeopathic remedy is made from the leaves.

Material uses

A yellow-gold dye is obtained from the stalks.

Habitat

Shallow water in ponds, ditches etc and in wet places on land.

Native range

Europe, including Britain, from Norway south and east to N. Africa and temperate Asia.

Scientific synonyms Persicaria hydropiper, Persicaria maculosa