Plant Base Online (beta)
common name: Japanese Knotweed
synonyms: Polygonum japonica
growth rate: very fast
leaf colour: green
flower colour: white
stem/bark: red & green
main season: Autumn
full sun, part shade, shade
dry soil, moist soil, wet/waterlogged soil, clay soil, sandy soil, coastal
preferred soil pH: any
minimum temp: -20°C
USDA zone: 5 to 9
Notoriously invasive weed, this is a robust and vigorous perennial, spreading by creeping underground rhizomes which produce hollow, arching, reddish stems with large, pointed heart-shaped leaves. Forms dense thickets. Branched clusters of greenish-white, sometimes pink, flowers from late August to October. Rarely sets seed.
Prefers moist soils but appears to thrive almost anywhere.
Originally introduced to Britain as an ornamental plant and very occasionally still used as such, particularly in difficult locations where adverse conditions restrict its spread.
Native to Japan but naturalised in other areas, including Britain, where it is common on waste-ground, road verges, by railways and streamsides.
Once established it is very difficult to eradicate.
Listed as potentially invasive in the UK (Wildlife and Countryside Act, Schedule 9)