Polygonum sachalinense - Giant Knotweed

Family:	Polygonaceae
Habit:	Perennial
Height:	3.6
Width:	3
Synonyms:	Reynoutria sachalinensis. (Freidrich.Schmidt.&Petrop.)Nakai.
Range:	E. Asia - Japan. Occasionally naturalized in Britain[17].

Polygonum sachalinense (Giant Knotweed) is a Perennial which grows to a height of 3.6m and a width of 3m . It has a fast growth rate. It has a hardness rating of 5.
Giant Knotweed will flower in January to April. the seeds ripen from February to April
The flowers from this plant are dioecious (each plant is either male or female, thus both genders need to be present to seed) and they are pollinated by

Soil Information

Giant Knotweed will grow in light (sandy),medium (loamy),hard (clay) soil. It is not necessary for the soil to be well drained.
The soil prefers the following PH / acid levels :
- pH of less than 6, Acidic soils
- pH between 6 and 8, Neutral soils
- pH greater than 8, Basic soils
Giant Knotweed prefers moist soils

Ideal Planting Locations

Giant Knotweed can grow in semi or areas with no shade.

Along ravines and by streams in montane areas of Sakhalin Island[58].

Planting places suited to this plant described below.

• Grows within a woodland garden
• Works within dappled Shade
• Grows in a shady edge
• Can spread to cover ground and will out compete weeds

Cultivation Details

Succeeds in ordinary garden soil in sun or shade[1, 111]. Hardy to about -25°c[187]. 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[233]. Dioecious, male and female plants must be grown if seed is required.

Edible Uses*

* See disclaimer
Edible Rating: 2/5
Young shoots in spring - raw or cooked[46, 61, 116, 183]. They can be added to salads or cooked as an asparagus substitute[183]. 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[183]. Seed - cooked[105]. 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.

• Leaves -
• Seed - includes nuts, cereals, peas and beans.
• Stem - this often intergrades into leaves.

Medicinal Uses*

* See disclaimer
Medicinal Rating: 0/5
None known

Propagation

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.

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[238].

Other Uses

A potential source of biomass. Plants are very vigorous and could be grown as a ground cover[208].

• Biomass - Provides a large quantity of plant material that can be converted into fuel etc.
• Ground cover - Usually low growing plants that can be grown with other plants, especially shrubs and trees, to prevent the growth of weeds.

Cultivars

no recorded cultivars

References

Flora of the British Isles.
Clapham, Tootin and Warburg.
Author: Clapham, Tootin and Warburg.
Rating:
Publisher : A very comprehensive flora, the standard reference book but it has no pictures.
Date of Publication : 1962

Flora of Japan. (English translation)
Ohwi. G.
Author: Ohwi. G.
Rating:
Publisher : The standard work. Brilliant, but not for the casual reader.
Date of Publication : 1965

The New RHS Dictionary of Gardening. 1992.
Huxley. A.
Author: Huxley. A.
Rating:
Publisher : Excellent and very comprehensive, though it contains a number of silly mistakes. Readable yet also very detailed.
Date of Publication : 1992

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