How To Rid Your Garden of Japanese Knotweed

A plant so dangerous it has put people in jail, if you see this biological terror, here's what to do

Credit: Jennifer Grenz?

Japanese knotweed

This aggressive pest can be tricky to get rid of

Invasive and resilient, learn how to get rid of Japanese knotweed

In the U.K. you may go to prison for growing or transporting it. Not surprisingly, it is considered the number-two most dangerous invasive, after giant hogweed.

Japanese knotweed (Polygonum cuspidatum) wreaks biological havoc: it rapidly out-competes native-plant species but has no food or habitat value for indigenous insects, birds or animals. 

In winter, plants lose their foliage, leaving large patches of soil exposed – this has resulted in slides, erosion of stream banks and fish death due to turbidity. Knotweed’s roots can stretch 3 m (10 ft.) deep and up to 20 m (65 ft.) lengthwise. It easily grows through concrete, thus threatens costly infrastructure like freeways. 

If you have this thug on your property, dig out smaller plants and be sure to get all pieces of root and stem, as it will grow from a tiny fragment of either, as well as from the abundant seed each knotweed produces if allowed. Do not mow! Dispose of plant material into the garbage (trash), not the green waste or compost; fragments of the plant can remain viable at temperatures over 100°C (212°F). For dealing with larger plants, ask for advice at or 604-880-8358.