Invasive Knotweeds In BC – Know Before You Buy Or Sell

This resilient superweed can grow through concrete foundations, walls driveways and roads. Its said the plant can push through concrete a couple metres thick. It can grow from only a few milligrams of root fragment so mowing or weedwacking it can spread it like wild fire. Herbacide is really the only effective way to remove it.

The problem has become so acute, it risks crossing the line from nuisance to serious financial liability. Its advised you are selling a home to disclose to the Buyer if you have the weed on your property. If you are buying a home get it checked out before you make the offer or make it a subject in the contract.

In the U.K., which has its own knotweed problem, some banks are refusing to give mortgages to homebuyers if the property is infested with the weed.

Japanese Knotweed (Fallopia japonica)

Although the primary knotweed species found in BC is Japanese knotweed (Fallopia japonica), Bohemian knotweed (Fallopia x bohemica), Giant knotweed (Fallopia sachalenensis), and Himalayan knotweed (Polygonum polystachyum) are also present and all four species are considered invasive. Since all four species are similar in appearance, biology, impacts, distribution, and methods of control, they will be discussed under the general title of “knotweeds”.


Bohemian knotweed is the hybrid of Japanese and Giant knotweeds. During the 2006 identification survey it was suspected that the most dominant knotweed species in BC was the hybrid Bohemian.






  • Native to eastern Asia
  • Small green-white flowers grow in showy plumes off stem and leaf joints
  • Stems are hollow and bamboo-like, with reddish-brown speckles
  • Leaves are heart-shaped and 8-10 cm across
  • Zig-zag pattern of leaf arrangement on the stem
  • Grow just about anywhere including waste sites, along roads, in meadows and wooded areas and along streambanks

Consequences of Invasion

  • Dominate stream banks
  • Increases erosion
  • Degrades wildlife and fish habitat
  • Reduces sight lines and block access to water bodies for recreation
  • Can grow over 3 m in a year
  • Able to grow through cement, house foundations, and walls
  • Extensive root systems are capable of resprouting even after many years of control
  • Roots can break off and float downstream to form new infestations

Prescription for Control

  • Cutting is not effective
  • Most effective way to eliminate it is to use a stem injector to inject stems with herbicide
  • Very important to control sprouts in new areas
  • Will not compost effectively
  • Must be bagged and buried deep in a landfill
  • Must be managed consistently through the growing season

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