What is Japanese Knotweed?

Japanese Knotweed, as the name may suggest, is foreign to Scotland. Japanese Knotweed was introduced from Japan to the Western world in the 1840s and by the 1850s had made its way to The Royal Botanic Gardens in Edinburgh. Today Japanese Knotweed is portrayed as a highly invasive and destructive plant because of its ability to grow densely and shade out native plants. Japanese Knotweed is commonly be found growing along watercourses which comes with various implications such as riverbank erosion and blocked watercourses. However, with its root growing between two meters deep and seven meters wide underground it can be just as problematic the natural landscape as build environments.

To find out more about Japanese Knotweed read our blog covering myths and facts about the highly invasive plant species and how to identify if you have Japanese Knotweed on your property.

What can you do about Japanese Knotweed?

Our certified staff offer treatments to control and eradicate Japanese Knotweed to prevent the chances of the invasive plant spreading to new areas. There are a number of ways you can tackle Japanese Knotweed; chemical spraying, stem injection or burning.

Chemical Spraying

Spraying with chemicals (herbicides) is an effective method of treatment to stop the spreading of the plant. This can’t be carried out when it’s raining or in windy conditions and has the potential of affecting other plants and soil. The plants should ideally be sprayed in the spring when they are about 1 meter tall or after cutting when they have re-grown to this height. Effective control can be achieved when the Japanese Knotweed is cut or sprayed again in early summer, then sprayed again in late summer, just before the winter dieback. The arisings from cutting should be burnt on-site to prevent the plant spreading.

Stem injection

Stem injection is a method of treatment where the herbicide is directly injected into the lower part of the mature stems using an injection gun. This method can be carried out in most weather conditions unlike the spraying method. As this method is to inject the plant it can be an environmentally friendly method of control, you will not have to worry about the chemicals used spilling into any watercourses or causing damage to any protected species/trees nearby because the measured does go directly into the stems.


Using a burning method is where we typically burn away the weed and has the benefit of not contaminating any other soil or plants. It requires more than one treatment as the root system can be 7 metres long and 2 metres deep and it is imperative that all the roots are destroyed to eradicate the weed.

Not sure if you may have Japanese Knotweed? Get in touch with us today and we'll provide a free site visit and quote.

Our experienced team have the knowledge to plan the best course of actions for removing Japanese Knotweed from your property. Still not sure, click here to see some of our Japanese Knotweed eradication projects.

Along with Japanese Knotweed eradication WCC Group offer a variety of grounds maintenance services in Helensburgh and it's surrounding area.