Know what you grow: Knotweed an invasive species

Knotweed rapidly invades shoreline, river-bank, and stream-bank habitats, where it blocks sunlight.

Knotweed rapidly invades shoreline, river-bank, and stream-bank habitats, where it blocks sunlight, disturbs nutrient cycling, displaces native vegetation, and increases stream-bank erosion. Try these instead: Goats Beard (Aruncus dioicus), Black Elderberry (Sambucus racemosa var. melanocarpa), and Oceanspray (Halodiscus discolor).

In the coming weeks, Knotweed plants that have spread their roots and stems over the last few months will begin producing delicate white flowers throughout the region. Be sure to know how to identify the Knotweed varieties in our area to help stop the spread of these invasive plants.

There are four different species of knotweed infesting British Columbia; Japanese, Himalayan, Bohemian, and Giant Knotweed. These bamboo-like plants, have become one of the most prolific invasive plants in the world with serious infestations in the United Kingdom, United States of America, and even here in Canada. In fact, stiff regulations and policies have been developed within the United Kingdom to help address their Knotweed issues.

Within the Cariboo Regional District (CRD), Knotweed is a regulated plant species under the BC Weed Control Act and the CRD’s Invasive Plant Management Regulation Bylaw.

Knotweed has the ability to spread very quickly because of its extensive root system which can reach 15–20 metres in length. Growth of new shoots can emerge up to 20 metres away from the parental plant and when disturbed, a hormone in the plant is released stimulating the growth of new shoots.

Knotweed spreads predominantly through a creeping root system; however it can also spread by seed. It can grow from one to five metres tall and crowds out native plants and habitat. Young shoots generally begin to emerge in May and growth rates of eight centimetres per day have been recorded. Knotweed has been observed to grow in environments without sunlight, through building foundations and through five centimetres of asphalt. It is a huge threat to species diversity and wildlife habitat.

Knotweed is no longer sold in nurseries, but is still spread through the sharing of garden plants, contaminated soil, and root fragments drifting downstream in water.

Knotweed has been found throughout the Cariboo Chilcotin and mostly in gardens, but recently many new plant sites have been found in unauthorized garden waste dump sites.

To keep this species from causing widespread impacts in the region, it is important to prevent its establishment in the first place. Do not purchase, trade, or grow Knotweed as there are better alternatives available including native plant species.

If you have Knotweed growing in your garden it is important to care for it in a manner that is not going to cause further spread.

Be sure to phone the Cariboo Regional District for advice on treating and disposing knotweed to ensure it is handled correctly.

If you have any questions or concerns about Knotweed or need some assistance in identification or management, please contact the CRD’s Invasive Plant Management department at 250-392-3351, or toll free at 1-800-665-1636, or visit our website at or on Facebook at

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