Japanese Knotweed

About the Plant

Japanese knotweed (Fallopia japonica) belongs to the plant family Polgonaceae. "Poly" means many and "gony" is from the Greek for "knee", giving many jointed. In Ireland Japanese knotweed is a non-native, alien invasive plant species, orginally from Japan & Northern China. It was introduced as an ornamental plant 19th century where it soon made its way to a variety of habitat types across the country. Please click here to its widespread distribution.

Japanese Knotweed changes in appearance from summer to winter which could cause confusion. In the summer time the plant is a lush green colour where each leaf is oval with a pointed-tip, and have a distinctive zig-zag pattern along the stem. The stem structures are also distinctive with a green hollow/bamboo-like appearance and are dotted with dark blue-purple speckles.  It forms small clusters of off white/yellow cream coloured flowers in late summer, typically forming from late July onwards. However in the winter time the stems die back and become an orange-brown colour.  These canes remain upright throughout the winter and can still be seen amongst new stands the following spring or summer.

  • Spring Growth

  • Summer

  • Winter

  • Flower

  • Leaves

  • Stems

  • Rhizome

If you see Japanese knotweed

DO NOT cut and discard plant

Do NOT dig it out 

Do NOT mow, strim or hedge-cut

Call Greeentown Environmental Ltd

Japanese Knotweed damage - Invading your property since 1840

Japanese Knotweed can cause significant damage to construction work and has the power to grow through tarmac, paving stones, brickwork and cement. If left untouched Japanese Knotweed will out compete and smother are native species. The plant’s leaf canopy of broad leaves obstructs light to the ground preventing natural flora and fauna from growing. Dead vegetation decomposes slowly over a number of years and also obstructs light. It also creates a fire risk during the Summer months and during dry periods. The plant can survive extreme heat and is found in volcanic areas within its natural habitat so burning Japanese Knotweed will not eradicate it. Japanese Knotweed has an extraordinary ability to spread vegetatively from crown, stem and rhizone if disturbed. All it takes is is a piece of rhizome less then 0.7g to grow a new plant.

Legislation: Law & Acts

Japanese knotweed is governed by numerous laws and acts concerning the way in which it is treated and disposed of, due to its damaging ability to spread aggressively if mishandled.

The Wildlife Order (NI) 1985

In Northern Ireland The Wildlife Order (NI) 1985 (as amended) states that it is an offence under Article 15 if anyone plants or otherwise causes to grow in the wild any species of plant listed on Schedule 9 Part II.

Management by Greentown Environmental Ltd

FAQ's

There`s a patch of Japanese Knotweed growing up through my lawn, is it okay to mow it?

No. By mowing Japanese Knotweed you may be creating plant fragments that could then be spread to other areas of your garden where it could grow.

There is an infestation of Japanese Knotweed on a neighbouring property and it is spreading into my land, who is responsible to get rid of it?

The landowner is responsible to ensure that they are not causing or allowing it to be dispersed or spread and should take action to control it. It is an offence for anyone to cause or allow it to be dispersed or spread. 

There is Japanese Knotweed growing in my community, who should I tell?

If possible, notify the land owner of the presence of the plant and its potential impact. If the plant is on public property you should inform the city council.