Giant knotweed

Fallopia sachalinensis


Photo credit: ©RPS group PLC; GBNNSS
Fallopia sachalinensis
  • Giant knotweed is a terrestrial plant found  across many habitats, including disturbed areas, roadsides, forests, and grasslands.
  • It may also be found in some littoral habitats, like coastal dunes.

  • Giant knotweed is a tall perennial plant, measuring 2-5m in height, and up to 5m.
  • Its stems are clustered, erect and rarely branching.
  • The leaves are ovate to oblong, measuring up to 40cm long and up to 25cm wide.
  • The flowers are bisexual and are greenish in colour. They are up to 6.5mm long with a stipe-like base.
  • Download N.I.E.A. ID guide

Origin and Distribution:
  • Giant knotweed is native to Japan (only northern Honshu and Hokkaido), Russia (Sakhalin Island only). It is possibly native to Ullung-do, an isolated island between Korea and Japan.
  • It is present in South Africa, Austria, Belgium, Bulgaria, Czechia, Denmark, Estonia, Finland, France, Germany, Greece, Ireland Italy, Poland, Norway, the United Kingdom (both Great Britain and Northern Ireland), the United States, Australia and New Zealand.

  • Once established, giant knotweed spreads rapidly through vegetative means. It tolerates a wide range of habitats, and can outgrow and outcompete native plants. It is difficult to control once established in an area.
  • It also has the ability to affect the germination of other plants by producing chemicals to inhibit their growth.

How could it get here?:
  • Giant knotweed was brought to Great Britain in the late 1860s as an ornamental plant, and was further spread as a food plant for livestock.
  • It could further be spread by contaminated soils.

Is it found in Ireland or Northern Ireland?
  • Yes, giant knotweed is currently in both Ireland and Northern Ireland.

You can help by reporting any sightings:   
Prevent Spread/Arrival
  • Follow Check Clean Dry protocols to ensure that this plant isn't accidently introduced or spread further.
  • Report all sightings

Current legislative position 
  • This species is on Schedule 9 of the Wildlife (Northern Ireland) Order 1985. It is against this order to plant or allow to grow in the wild any plant (or hybrid of any plant) listed in Schedule 9.

Species Related Files:

Invasive Species Ireland

Invasive Species Ireland