Practical
Plants

Polygonum sachalinense

Giant Knotweed

a perennial member of the Polygonum genus in the family Polygonaceae.

No photo available

Taxonomy and growth

Life cycle
perennial
Growth rate
vigorous
Height
3.6 m
Spread
3 m
Fertility
self sterile
Flower type
dioecious

Uses

Toxicity

Toxicity warning. The historical record reports a hazard for this plant. Do not use it to decide which parts are safe to eat or use medicinally.

This section contains historical Plants For A Future notes marked noncommercial.

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[11].

Edible uses

This section contains historical Plants For A Future notes marked noncommercial.

Young shoots in spring - raw or cooked[12][14][4][6]. They can be added to salads or cooked as an asparagus substitute[6]. They have an acid flavour and we find that they are more like a rhubarb substitute. Older stems and shoot tips - cooked. The stems are best peeled. Tasting like a mild version of rhubarb, they have a superior quality with a hint of lemon in the flavour[6]. Seed - cooked[2]. The seed can be ground into a powder and used as a thickener and flavouring in soups etc, or as an extender in flour. It is rather small and fiddly to utilize.

Plant part
Leaves
Plant part
Seed
Plant part
Stem

Material uses

This section contains historical Plants For A Future notes marked noncommercial.

A potential source of biomass. Plants are very vigorous and could be grown as a ground cover[9].

Product or use
Biomass

Ecology and functions

Ecosystem niche
Soil surface

Ground cover

Environment

Range
E. Asia - Japan. Occasionally naturalized in Britain[5].
Habitat
Along ravines and by streams in montane areas of Sakhalin Island[13].
Light
full sun
Shade tolerance
light shade
Water
moderate
Hardiness
Zone 5+
Soil textures
sandy, loamy, clay
Soil pH
acid, neutral, alkaline
Tolerates Nutritionally Poor Soil
No
Drought
intolerant

Propagation

This section contains historical Plants For A Future notes marked noncommercial.

Seed - sow spring in a cold frame. 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. Division in spring or autumn. Very easy, larger divisions can be planted out direct into their permanent positions. We have found that it is better to pot up the smaller divisions and grow them on in light shade in a cold frame until they are well established before planting them out in late spring or early summer.

Cultivation

This section contains historical Plants For A Future notes marked noncommercial.

Succeeds in ordinary garden soil in sun or shade[1][3]. Hardy to about -25°c[7]. An extremely invasive plant, capable of sending up new shoots at a considerable distance from the main clump[1]. 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[10]. Dioecious, male and female plants must be grown if seed is required.

References

  1. F. Chittendon. RHS Dictionary of Plants plus Supplement. 1956 Oxford University Press 1951-00-00

    ↩1↩2

  2. Tanaka. T. Tanaka's Cyclopaedia of Edible Plants of the World. Keigaku Publishing 1976-00-00

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  3. Sanders. T. W. Popular Hardy Perennials. Collingridge 1926-00-00

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  4. Brooklyn Botanic Garden Oriental Herbs and Vegetables, Vol 39 No. 2. Brooklyn Botanic Garden 1986-00-00

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  5. Clapham, Tootin and Warburg. Flora of the British Isles. Cambridge University Press 1962-00-00

    ↩

  6. Facciola. S. Cornucopia - A Source Book of Edible Plants. Kampong Publications 1990-00-00 ISBN 0-9628087-0-9

    ↩1↩2↩3

  7. Phillips. R. & Rix. M. Perennials Volumes 1 and 2. Pan Books 1991-00-00 ISBN 0-330-30936-9

    ↩

  8. Huxley. A. The New RHS Dictionary of Gardening. 1992. MacMillan Press 1992-00-00 ISBN 0-333-47494-5

  9. Thomas. G. S. Plants for Ground Cover J. M. Dent & Sons 1990-00-00 ISBN 0-460-12609-1

    ↩

  10. Thomas. G. S. Perennial Garden Plants J. M. Dent & Sons, London. 1990-00-00 ISBN 0 460 86048 8

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  11. Bown. D. Encyclopaedia of Herbs and their Uses. Dorling Kindersley, London. 1995-00-00 ISBN 0-7513-020-31

    ↩

  12. Uphof. J. C. Th. Dictionary of Economic Plants. Weinheim 1959-00-00

    ↩

  13. Ohwi. G. Flora of Japan. (English translation) Smithsonian Institution 1965-00-00

    ↩

  14. Usher. G. A Dictionary of Plants Used by Man. Constable 1974-00-00 ISBN 0094579202

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