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Giant knotweed - Invasive Species Information

JKK - High Risk Sign Red 18.gif

What Is Giant knotweed - (Fallopia sachalinensis)?

Habitat: Terestrial
Distribution in Ireland: Abundant in some areas

Status: Established

Family name: Polygonaceae

Reproduction: Strong, extensively spreading rhizomes form large clonal colonies.


The species is gynodioecious, with male and female (male sterile) flowers on separate plants.

Giant Knotweed Through Tarmac Driveway

Giant knotweed growing through tarmac

Giant knotweed is a species of Fallopia native to north eastern Asia, northern Japan and the far east of Russia it was introduced to Ireland by gardeners and now resides in most counties across Ireland.  It is identified by the leaves which are some of the largest in the family, up to 15–40 cm long and 10–28 cm broad.

Giant knotweed is a herbaceous perennial plant. The flowers are small, produced on short, dense panicles up to 10 cm long in late summer or early autumn and grows to 4 meters high.


It is invasive and the impacts on the environment are significant.


The species is closely related to the Japanese knotweed - Fallopia japonica, and can be distinguished from it by its larger size with a  smooth edged, elongated heart-shaped leaf, with a slight wavy, crenate margin. 

How To Identify Giant knotweed?

Giant knotweed stems

Giant knotweed stems

Dwarf JK Leaf ID - Fallopia japonica var. ID Guide

Knotweed leaf size & shape comparison

Leaf: Large elongated heart shaped mat green appearance, with smooth edge

Flower: Small creamy/white flower

Stem: Hollow, mostly green with red banding

Size: Plant can grow to over 4 metres tall

Giant Knotweed Flower
Giant Knotweed leaf

Why Is Giant Knotweed A Problem?

Giant knotweed has a wide-ranging root system, which can extend up to 3m in depth and 7m in all directions.


These can pose a serious threat to construction works and have devastating consequences to building structures, foundations and drains.

Structural damage caused by untreated Giant knotweed can cause tens of thousands of euro's to rectify

Giant knotweed flower

Giant knotweed leaf

Giant Knotweed - Fallopia sachalinensis ID guide V4.gif

Giant knotweed - Fallopia sachalinensis ID Guide

European Communities (Birds and Natural Habitats) Regulations 2011 non-native invasive plant species A-Z (Updated 2017)

There are currently 35 invasive plant species listed in the European Communities (Birds and Natural Habitats) Regulations (annex 2, Part 1)...


Click on a species from the following list to find out more regarding non-native species subject to restrictions under Regulations 49 and 50.

  1. American Skunk-CabbageLysichiton americanus

  2. Brazilian Giant-RhubarbGunnera manicata

  3. Broad-Leaved RushJuncus planifolius

  4. Cape PondweedAponogeton distachyos

  5. Cord-GrassesSpartina (all species and hybrids)

  6. Curly Waterweed - Lagarosiphon major

  7. Dwarf Eel-GrassZostera japonica

  8. FanwortCabomba caroliniana

  9. Floating PennywortHydrocotyle ranunculoides

  10. Fringed Water-LilyNymphoides peltata

  11. Giant HogweedHeracleum mantegazzianum

  12. Giant knotweedFallopia sachalinensis

  13. Giant-RhubarbGunnera tinctoria

  14. Giant SalviniaSalvinia molesta

  15. Himalayan BalsamImpatiens glandulifera

  16. Himalayan KnotweedPersicaria wallichii

  17. Hottentot-FigCarpobrotus edulis

  18. Japanese KnotweedFallopia japonica

  19. Large-Flowered WaterweedEgeria densa

  20. Mile-a-Minute WeedPersicaria perfoliata

  21. New Zealand PigmyweedCrassula helmsii

  22. Parrots FeatherMyriophyllum aquaticum

  23. Red AlgaGrateloupia doryphora

  24. RhododendronRhododendron ponticum

  25. SalmonberryRubus spectabilis

  26. Sea-Buckthorn Hippophae rhamnoides

  27. Spanish Bluebell Hyacinthoides hispanica

  28. Three-Cornered LeekAllium triquetrum

  29. WakameUndaria pinnatifida

  30. Water ChestnutTrapa natans

  31. Water FernAzolla filiculoides

  32. Water LettucePistia stratiotes

  33. Water-PrimroseLudwigia (all species)

  34. WaterweedsElodea (all species)

  35. WireweedSargassum muticum

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