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Summary
Bloom Color: Pink. Main Bloom Time: Early fall, Late summer. Form: Upright or erect.
Physical Characteristics
Polygonum japonicum is a PERENNIAL growing to 3 m (9ft) by 5 m (16ft) at a fast rate.
See above for USDA hardiness. It is hardy to UK zone 5. It is in flower from July to October, and the seeds ripen from August to October. The species is dioecious (individual flowers are either male or female, but only one sex is to be found on any one plant so both male and female plants must be grown if seed is required). . The plant is not self-fertile.
It is noted for attracting wildlife.
Suitable for: light (sandy), medium (loamy) and heavy (clay) soils. Suitable pH: mildly acid, neutral and basic (mildly alkaline) soils. It can grow in semi-shade (light woodland) or no shade. It prefers moist soil.
UK Hardiness Map
US Hardiness Map
Synonyms
P. cuspidatum. Sieb.&Zucc. P. sieboldii.
Plant Habitats
Woodland Garden Dappled Shade; Shady Edge;
Edible Uses
Edible Parts: Leaves Root Seed Shoots Stem
Edible Uses:
Young shoots in spring - cooked. They can be used as an asparagus substitute[55, 62, 116, 1599, 179, 183]. They have an acid flavour and can also be used as a rhubarb substitute in pies, fruit soups, jams etc[183]. Older stems and shoot tips - cooked[62, 159]. They taste like a mild version of rhubarb[K]. Seed - raw or cooked. It is rather small and fiddly to utilize. The seed can also be ground into a powder and used as a flavouring and thickener in soups etc, or can be mixed with cereals when making bread, cakes etc. The root is sometimes eaten[183].
References More on Edible Uses
Medicinal Uses
Plants For A Future can not take any responsibility for any adverse effects from the use of plants. Always seek advice from a professional before using a plant medicinally.
Antiphlogistic Antitumor Depurative Diuretic Emollient Febrifuge Stomachic Vulnerary
Women's complaints
The root is antiphlogistic, bechic, depurative, diuretic, emmenagogue, emollient, febrifuge, stomachic and vulnerary[46, 61, 147, 178, 218]. It is also used in the treatment of women's complaints[147]. A decoction is used in the treatment of burn injuries, boils and abscesses, poisonous snakebites, acute hepatitis, appendicitis, traumatic injuries and menstrual irregularities[147]. The leaves can be crushed and applied externally as a poultice to abscesses, cuts etc, whilst the dried roots can be ground into a powder and applied externally[147]. Extracts of the plant have shown antitumour activity[218].
References More on Medicinal Uses
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Other Uses
Biomass Dye
A yellow dye is obtained from the root[46, 61]. The plant is potentially a good source of biomass. Plants can be grown to form a ground cover that will exclude all other growth[208]. It is best to use the sub-species compactum since this is less invasive[208].
Special Uses
Attracts Wildlife
References More on Other Uses
Cultivation details
Landscape Uses:Container, Specimen, Woodland garden. A very easily grown plant, it succeeds in ordinary garden soil in sun or shade[1, 111], though it prefers a moist soil in partial shade[187]. Japanese knotweed is an extremely invasive plant capable of sending up new shoots at a considerable distance from the main clump and also of growing up through tarmac[200]. The sub-species cuspidatum is the form that is most likely to cause problems. It is considered to be a pest in many areas, where it is forming large clumps in the wild and out-competing native species. If grown in the garden it should be planted within a strong barrier to contain its roots. The sub-species compacta is only about 70cm tall and is far less invasive, but should still not be grown in small gardens[200]. A report on the Natural History Programme stated that Japanese knotweed is actually becoming a very valuable habitat for spiders, frogs, grass snakes and many other creatures. Its hollow stems allow a wide variety of insects and other small creatures to overwinter and find hiding places, thus a greater abundance of food is provided for insectivores such as frogs, who are themselves eaten by grass snakes. In areas of north Wales where Japanese knotweed has run rife, it is now the primary habitat for grass snakes[215]. Plants seem to be immune to the predations of rabbits[233]. Often cultivated as a dye and a medicinal plant[46, 61]. Very closely related to P. conspicuum[58]. Dioecious, male and female plants must be grown if seed is required[58]. Special Features:Attractive foliage, Invasive, Wetlands plant.
References Carbon Farming Information and Carbon Sequestration Information
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Plant Propagation
Seed - sow spring in a cold frame. 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.
Other Names
If available other names are mentioned here
Native Range
Coming Soon
Weed Potential
Right plant wrong place. We are currently updating this section.
Please note that a plant may be invasive in one area but may not in your area so it’s worth checking.
Conservation Status
IUCN Red List of Threatened Plants Status :
| Related Plants
|
| Latin Name | Common Name | Habit | Height | Hardiness | Growth | Soil | Shade | Moisture | Edible | Medicinal | Other |
| Polygonum alaskanum | Alaska Wild Rhubarb | Perennial | 1.8 |
-
| | LMH | SN | M | 2 | 1 | |
| Polygonum alpinum | Alpine Knotweed, Alaska wild rhubarb | Perennial | 1.0 |
4-8
| | LMH | SN | M | 2 | 1 | |
| Polygonum amphibium | Willow Grass, Water knotweed, Longroot smartweed, Water smartweed | Perennial | 0.3 |
4-8
| | LMH | SN | WeWa | 1 | 2 | 1 |
| Polygonum arenastrum | Small-Leaved Knotweed, Oval-leaf knotweed | Annual | 0.3 |
4-8
| | LMH | SN | M | 2 | 3 | 1 |
| Polygonum aviculare | Knotweed, Prostrate knotweed | Annual | 0.3 |
4-8
| | LMH | SN | M | 2 | 3 | 1 |
| Polygonum barbatum | Joint Weed | Perennial | 0.8 |
-
| | LMH | SN | M | 1 | 1 | |
| Polygonum bistorta | Bistort, Meadow bistort, Snakeweed | Perennial | 0.5 |
4-7
| F | LMH | SN | MWe | 3 | 3 | 2 |
| Polygonum bistortoides | American Bistort | Perennial | 0.5 |
4-8
| | LMH | SN | M | 3 | 1 | |
| Polygonum bungeanum | Bunge's smartweed | Annual | 0.8 |
0-0
| | LMH | SN | M | 1 | 0 | |
| Polygonum coccineum | Water Smartweed | Perennial | 0.5 |
4-8
| | LMH | SN | WeWa | 1 | 0 | |
| Polygonum conspicuum | | Perennial | 0.6 |
-
| | LMH | SN | M | 1 | 0 | |
| Polygonum convolvulus | Black Bindweed | Annual | 1.2 |
0-0
| | LMH | SN | M | 1 | 0 | 0 |
| Polygonum divaricatum | | Perennial | 1.0 |
-
| | LMH | SN | DM | 1 | 0 | |
| Polygonum douglasii | Knotweed, Douglas' knotweed, Austin knotweed, Engelmann's knotweed, Johnston's knotweed, Large kno | Annual | 0.3 |
0-0
| | LMH | SN | DM | 2 | 0 | |
| Polygonum dumetorum | Climbing false buckwheat | Annual | 1.8 |
0-0
| | LMH | SN | M | 1 | 1 | |
| Polygonum equisetiforme | | Perennial | 1.0 |
7-10
| | LMH | N | DM | 1 | 0 | 2 |
| Polygonum fugax | | Perennial | 0.0 |
-
| | LMH | SN | M | 3 | 0 | |
| Polygonum hydropiper | Smartweed, Marshpepper knotweed | Annual | 0.8 |
0-0
| | LMH | N | WeWa | 2 | 2 | 1 |
| Polygonum lapathifolium | Curlytop Knotweed | Annual | 0.8 |
4-8
| | LMH | SN | MWe | 1 | 1 | 1 |
| Polygonum limosum | | Perennial | 1.8 |
-
| | LMH | SN | M | 1 | 0 | |
| Polygonum longisetum | Oriental lady's thumb | Annual | 0.5 |
0-0
| | LMH | SN | MWe | 1 | 0 | |
| Polygonum maackianum | | Annual | 0.8 |
-
| | LMH | SN | MWe | 1 | 0 | |
| Polygonum manshuriense | Asian Bistort | Perennial | 0.8 |
-
| | LMH | SN | Mwe | 0 | 1 | |
| Polygonum microcephalum | | Perennial | 0.5 |
-
| | LMH | SN | M | 1 | 0 | |
| Polygonum minus | Pygmy smartweed | Annual | 0.3 |
0-0
| | LMH | SN | MWe | 1 | 0 | |
| Polygonum molle | | Perennial | 2.5 |
6-9
| F | LMH | SN | M | 2 | 1 | 2 |
| Polygonum multiflorum | He Shou Wu, Tuber fleeceflower | Perennial Climber | 4.5 |
6-9
| | LMH | SN | M | 2 | 3 | |
| Polygonum nepalense | Nepalese smartweed | Annual | 0.3 |
0-0
| | LMH | SN | MWe | 1 | 1 | 1 |
| Polygonum orientale | Prince's Feather, Kiss me over the garden gate | Annual | 1.5 |
0-0
| | LMH | SN | M | 2 | 2 | 0 |
|
|
Growth: S = slow M = medium F = fast. Soil: L = light (sandy) M = medium H = heavy (clay). pH: A = acid N = neutral B = basic (alkaline). Shade: F = full shade S = semi-shade N = no shade. Moisture: D = dry M = Moist We = wet Wa = water.
Expert comment
Author
Meissn.
Botanical References
1758200
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