Polygonum sachalinense

F. Schmidt

Giant knotweed, Sakhalin Knotweed, Sachaline

Polygonaceae Edible: Leaves, Seeds Potential hazards — see below

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Summary

A vigorous perennial growing 3.6 m tall and 3 m wide at a fast rate, hardy to UK zone 5. Dioecious with male and female flowers on separate plants; flowering occurs July to October with seeds ripening August to October. Thrives in light sandy, medium loamy, and heavy clay soils across mildly acidic to mildly alkaline pH ranges. Adapts to semi-shade or full sun and prefers moist soil.

Description

Edible Uses

Young spring shoots can be eaten raw or added to salads, or cooked as an asparagus substitute. They have an acid flavour, though in practice they more closely resemble a rhubarb substitute. Older stems and shoot tips can be cooked after peeling; they taste like a mild, lemon-tinged version of rhubarb and are considered superior in quality. The seed can be cooked, ground into a powder for use as a soup thickener and flavouring, or used as an extender in flour. The seed is quite small and fiddly to work with.

Traditional Uses

The young shoots and tips are eaten raw in salads. They are also parboiled and served like asparagus. They can be used in soups. The peeled young stems are used for "rhubarb" sauce. The fruit is eaten. It is also stored in fish oil for later use.

Medicinal Uses

None known

Known Hazards

Although no specific mention has been made for this species, there have been reports that some members of this genus can cause photosensitivity in susceptible people. Many species also contain oxalic acid (the distinctive lemony flavour of sorrel) - whilst not toxic this substance can bind up other minerals making them unavailable to the body and leading to mineral deficiency. Having said that, a number of common foods such as sorrel and rhubarb contain oxalic acid and the leaves of most members of this genus are nutritious and beneficial to eat in moderate quantities. Cooking the leaves will reduce their content of oxalic acid. People with a tendency to rheumatism, arthritis, gout, kidney stones or hyperacidity should take especial caution if including this plant in their diet since it can aggravate their condition.

Distribution

It is a temperate plant.

Where It Grows

Asia, Britain, Europe, Japan, North America, USA,

Cultivation

Succeeds in ordinary garden soil in sun or shade. Hardy to about -25°c. An extremely invasive plant, capable of sending up new shoots at a considerable distance from the main clump. Considered a pest in many areas, if grown in the garden it should be planted within a barrier to contain its roots. Plants seem to be immune to the predations of rabbits. Dioecious, male and female plants must be grown if seed is required.

Propagation

Sow seed in spring in a cold frame. Germination is usually straightforward. Once seedlings are large enough to handle, prick them out into individual pots and plant out during summer if they have grown sufficiently. If not, keep them in a cold frame over winter and plant out the following spring after the last expected frosts. Division can be done in spring or autumn. Larger divisions can go directly into their permanent positions. Smaller divisions are better potted up and grown on in light shade in a cold frame until well established, then planted out in late spring or early summer.

Other Uses

The plant is a potential source of biomass. Its vigorous growth also makes it a candidate for use as ground cover.

Notes

There are about 50 Polygonum species.

Synonyms

Reynoutria sachalinensis

References (6)

Duke, J.A., 1992, Handbook of Edible Weeds. CRC Press. p 154
Elias, T.S. & Dykeman P.A., 1990, Edible Wild Plants. A North American Field guide. Sterling, New York p 99
Facciola, S., 1998, Cornucopia 2: a Source Book of Edible Plants. Kampong Publications, p 186 (As Reynoutria sachalinensis)
C. J. Maximowicz, Mem. Acad. Imp. Sci. St.-Petersbourg Divers Savans 9:233. 1859 (Prim. fl. amur.)
Plants for a Future database, The Field, Penpol, Lostwithiel, Cornwall, PL22 0NG, UK. http://www.scs.leeds.ac.uk/pfaf/

Show all 6 references