Ecology

Japanese Knotweed

About Japanese Knotweed

Invasive non-native species (INNS) in the UK under Schedule 9 of the Wildlife and Countryside Act. Therefore, “it is an offence to plant or otherwise cause to grow these species in the wild.” The leaves are green and in the shape of a spade head. The stem grows in a zig-zag shape.

The Problem

Much like other invasive species, Japanese Knotweed grows in dense clumps causing it to outcompete native British plants and reduce plant diversity. Losses in native plant diversity can lead to changes in habitat and loss of native wildlife.
Japanese Knotweed can grow as much as 10cm per day. Rather than being spread by seed dispersal, Japanese Knotweed is spread from chopped stems or roots (rhizomes). This can happen when soil containing the roots is relocated.
Due to fast growth rates the plant can damage buildings, structures, tarmac and paving, as the plant attempts to grow through them, causing cracks and crumbling.
The roots can grow up to 3 metres deep and 7 metres across in all directions. Therefore, underground structures such as pipes and electric cables are also put at risk of blocking or damage.
Japanese Knotweed is treated as controlled waste. If it is growing on your land, you cannot be prosecuted but if it spreads further then you may be prosecuted.

The solution

Japanese Knotweed has tough roots and if they are left in the soil then the plant will regrow. Therefore, the only way to irradicate the plant is by spraying or injecting the stems with chemicals.

Approved herbicides must be applied by a ‘Competence for Herbicide Use’ certificate holder. The qualified individual may then compost, bury, or burn the blackened stems, in conformance with the Environmental Agency. This process will normally occur annually, up to three times.