Practical
Plants

Polygonum douglasii

Knotweed

an annual member of the Polygonum genus in the family Polygonaceae.

No photo available

Taxonomy and growth

Life cycle
annual
Height
0.3 m
Fertility
Insects
Flower type
hermaphrodite
Pollinators
Insects

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[8].

Edible uses

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

Leaves - raw or cooked. Seed - dried then ground into a powder and mixed with cornmeal or other cereals for making bread etc[11][13][2][3][9]. The seed is rather small and fiddly to utilize, it is enclosed in a dry papery hull[5].

Plant part
Leaves
Plant part
Seed

Environment

Range
N. America - Northwest Territory to British Columbia, south to Vermont, New Mexico and Oklahoma.
Habitat
Rocky slopes and dry soils all over N. America[10][12].
Light
full sun
Shade tolerance
light shade
Water
moderate
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.

We have very little information on this species and do not know if it is hardy in Britain, though judging by its native range it should succeed outdoors in most parts of the country. The following notes are based on the general needs of the genus. Succeeds in an ordinary garden soil[1] but prefers a moisture retentive not too fertile soil in sun or part shade[4]. Repays generous treatment[1]. Plants seem to be immune to the predations of rabbits[6].

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. Yanovsky. E. Food Plants of the N. American Indians. Publication no. 237. U.S. Depf of Agriculture.

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

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  5. Coffey. T. The History and Folklore of North American Wild Flowers. Facts on File. 1993-00-00 ISBN 0-8160-2624-6

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

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  7. Britton. N. L. Brown. A. An Illustrated Flora of the Northern United States and Canada Dover Publications. New York. 1970-00-00 ISBN 0-486-22642-5

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

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  9. Moerman. D. Native American Ethnobotany Timber Press. Oregon. 1998-00-00 ISBN 0-88192-453-9

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  10. Fernald. M. L. Gray's Manual of Botany. American Book Co. 1950-00-00

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

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  12. Hitchcock. C. L. Vascular Plants of the Pacific Northwest. University of Washington Press 1955-00-00

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

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