Japanese Knotweed

Japanese knotweed is not accepted at Recycling Centres

It is one of the 100 worst non-native invasive species in the world. It was introduced in the 19th century, as an ornamental plant from Japan, but is now spreading rapidly throughout the British Isles and is causing problems in the Derry City Council area.
 

How to recognise it

It has vigorously invaded green spaces and out-competes native vegetation, by reducing light. It forms extensive dense stands, with vertical green leafy shoots that extend up to 3 m in height above the parent plant and are large, broadly oval and pointed, usually with a pale stripe down the middle of the leaf.

It produces long strings of creamy-white flowers that arise from the tips of the stems. It dies back in autumn, but persists as brown withered leafless canes during the winter, which leaves the ground bare and more susceptible to erosion.

How does it spread?

It is associated with a deep, extensive rhizome network, which extends up to 7 m beyond the parent plant. Rhizomes range from 5 to 100 mm in diameter, are fleshy to woody, reddish to dark brown externally, with a distinct internal orange colour. The roots are fine, white and thread-like. It is spreading quickly throughout Ireland, with the main method of distribution, from the movement of soil material infected with fragments of rhizome (root) or plant material. It requires as little as 0.7 g present in soil, to allow it to rejuvenate. Also, it is spread by contaminated vehicles, equipment, colonisation from upstream areas, washing it downstream and illegal dumping.

Why is it a problem?

It is recognised as an expensive maintenance problem, as its shoots penetrate impermeable surfaces, which causes serious damage to buildings, walls, roads, footpaths and it blocks drains. Banks are refusing to grant mortgages for properties, where it is present, as it is a long term and expensive process to eradicate.

Under Schedule 9 of the Wildlife Order (NI) 1985, it is an offence to plant or cause it to grow in the wild. This places a duty of care to prevent the further spread to adjacent land. The Department of the Environment’s policy on disposal of Japanese knotweed material and contaminated soils, places a duty of care on all waste producers, to ensure Japanese knotweed is disposed of at a licensed landfill site that accepts it.

Derry City Council does not accept Japanese Knotweed at any of its Recycling Centres.

For further information contact Derry City Council’s Biodiversity Officer on 02871 365151 or email christine.doherty@derrycity.gov.uk