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Japanese knotweed

Invasive Species Information

Japanese Knotweed Fallopia japonica - Biodiversity High Risk 20

What Is Japanese knotweed (Fallopia japonica - Gliúneach bhiorach)?

Habitat: Terrestrial. Commonly found along river banks, roadsides, urban areas, waterways and railways. Likes disturbed ground.

Distribution In Ireland: Extensive and widespread

Status: Established

Family name: Polygonacae

Reproduction: Speeds through vegetive means. Fragments of rhizome or stem.

Native to Japan and parts of South East Asia, Japanese knotweed is used to extremely harsh conditions. In it's native enviroment it can be found growing on the side of volcanic mountains and has a very hardy perennial growth cycle. Japanese knotweed and it's hybrids are now widely distributed across Ireland causing a major management concern for public authorities and private property owners.

Japanese knotweed images

Japanese knotweed has no natural predators in Ireland and thrives in wet land conditions. It can spread from root fragments left behind when ground is disturbed, which is why it can often be found along waterways and at road sides.

How to Identify Japanese Knotweed?

Japanese Knotweed ID Guide

Japanese knotweed - Fallopia japonica ID Guide

ColourVibrant Green

Leaf: Bright Green, spade shape

Flower: Creamy white, delicate & small

Stem: Red/purple & green, hollow (similar to bamboo)

Root: Tough, orange/brown with white shoots

Jpanese Knotweed Autumn Leaves
Japanese Knotweed Winter Canes

Japanese knotweed autumn leaf & stem

Why Is Japanese Knotweed A Problem?

Japanese knotweed has become a serious problem in Ireland and many other parts of
Europe due to it's aggressive spread and speed of growth causing extensive damage to buildings and structures.


Having Japanese knotweed can seriously effect the value of properties and prevent the approval of planning permission for site development.

Japanese knotweed Time-Lapse Video

Japanese Knotweed Crown (Labelled)
Knotweed Identification Guide

Japanese knotweed

Fallopia japonica - Gliúneach bhiorach

Japanese Knotweed In Flower

Japanese knotweed is one of the most problematic invasive alien species in Ireland becoming a common sight on rural properties, waterways, roads and in wetland habitats.


It is classified as one of the top 100 worst invasive species worldwide due to its serious impact on biological diversity, impact on human activity and its capacity to invade new environments.

Japanese knotweed Leaf & Flower

Knotweed is now widely distributed across Ireland and is a major management concern for public authorities and private property owners.

Japanese Knotweed Growth Cycle

Japanese knotweed growth cycle

Japanese Knotweed Stand
Japanese Knotweed Shoots Breaking Through Tarmac

New shoots breaking through tarmac

Once established Japanese knotweed can grow at a veracious rate, establishing a root system that can spread up to 7 metres from the plant surface and up to 2 metres down.


The rhizomes (nodes on the plant root) are packed with energy and can remain dormant for up to 20 years!


Japanese knotweed is relentless in growing through almost any barrier. It has no problem breaking through weak concrete, brick, paving slabs and tarmac and will push its way to the surface at an alarming rate. 


The impact on properties can be devastating.

Japanese knotweed can quickly establish dense standings

Japanese knotweed Removal

If you discover Japanese knotweed on your property the first thing you will probably do is to try to find out how to get rid of it.


Having Japanese knotweed on your property is enough to strike dread into the heart of any property owner, bearing in mind all the negative media coverage that it has gained during the past few years.


Property buyers and developers have experienced difficulties securing mortgages for properties affected by Japanese knotweed and some lenders reject outright any property affected by knotweed, others take a more practical view and lend where the infestation is being treated.

Japanese knotweed thrives on disturbance and invades environments where soils are routinely disturbed and transported.

  • Do not strim, cut, flail or chip the plants as tiny fragment can regenerate new plants and make the infestation harder to control

  • Do not attempt to dig out Japanese knotweed, this can actually encourage the plant  into growing faster, therefore colonising an area more aggressively

  • Do not move or dump soil which may contain plant material as this may also add to its spread

  • Do not attempt to pull the plant out of the ground, as this can expose part of the infectious crowns, stimulating growth

  • Do not use unlicensed herbicides close to any watercourses, plants or wildlife

  • Do not compost any part of the plant, due to the resilient nature of knotweed it could survive and grow on when the compost is ready for use

  • Do not dispose of Japanese knotweed in garden waste allotments as this just transports the plant to new locations

  • Do not spread any soil that has been contaminated with Japanese knotweed rhizome as new plants will sprout

  • Do not do break the law! – Remember, it is an offence if you cause the spread of Japanese Knotweed either intentionally or unintentionally

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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