Everything you need to know about Japanese Knotweed

The background:

‘Fallopia Japonica’, AKA the ‘Japanese Knotweed’, was originally located in Eastern Asia on the side of volcanoes. It was first introduced to Europe as an ornamental plant in the early 1800’s. Following an increasing understanding of Japanese Knotweed, it became recognised as one of the most quickly spreading weeds in Europe, and arguably one of the worsts plants you can possibly find in a property you reside in.

A front garden being taken over by Japanese Knotweed.

What makes it so bad?

Japanese Knotweed has a number of attributes that result in it being so difficult to eradicate. Firstly, it will last for an indefinite number of years. It can also expand up to 2 meters in one summer, with the visible part of the plant usually growing up to 3-4 meters long. It’s roots can grow up to 7 meters down, so typically the part that is not visible will be a great deal larger. It can cause physical damage to property structures by damaging garden walls, damaging drain pipes and growing through floors. Because the plant can grow so vigorously, it can dominate a garden and suppress the development of other plants. Despite it being so active in the summer, when the winter comes the visible part of the plant will die. Unfortunately, under the ground it will still remain healthy and grow back the following Spring.

What does it look like?

The first signs of Japanese Knotweed would usually arise in early springtime. Distinctive red and purple shoots can rise from ground level. By early summer the plant will start to grow at its quickest rate, and at this point will have a bamboo like stem. The leaves appear in a heart shape, and will grow from the stem in a zig-zag pattern. By Autumn time the leaves will darken and slowly start to deteriorate. The plant will appear dead by the winter, however the canes the plant leaves can stay there for months, and by early Spring the cycle will repeat itself.

A Japanese Knotweed plant in the height of summer.

What are the main ways to eliminate it?

Despite it having a bad reputation, there are certain ways you can remove the plant for good, without using the assistance of a professional. Digging it out at times can be a viable option. The roots, however, can grow so far under the ground that you may have to bring in a professional to perform the digging successfully. The idea behind digging the plant out is by removing the ‘Rhizomes’, which are the network of underground stems. Despite being a big job due to the sheer volume of space the Rhizomes take up underground, digging out Japanese Knotweed remains one of the best ways to eliminate the plant. It’s vital to remember that you must dispose of Japanese Knotweed in a licensed landfill. Technically it is classed as ‘controlled waste’, therefore disposing of it incorrectly can result in criminal prosecution.

Weedkiller, when used correctly for an appropriate period of time, can also dispose of Japanese Knotweed. It is recommended to use professional help if this is your chosen method, as they will have access to stronger weed killer. Trying to eliminate the plant with household weed killers is possible, but even if done correctly takes 3-4 years to eradicate.