Invasive exotic plants and control measures – Part 1: Japanese knotweed

Japanese knotweed is an invasive exotic plant native to East Asia. Its spread must be prevented.

Japanese knotweed colony (source: MELCC)

Japanese knotweed is a fast-growing herbaceous perennial often found on residential lots as an ornamental plant. It colonizes a wide variety of soils and prefers open areas such as:

  • riverbanks,
  • roadsides and railroad,
  • wasteland,
  • gardens.

The formation of dense colonies prevents the growth of other plant species, so that invaded environments have very low species diversity. Japanese knotweed can also promote shoreline erosion, altering the chemical composition of the soil and the diversity of microorganisms found there. It restricts access to riverbanks, as well as openings to the landscape. Its roots and stems can also infiltrate cracks in infrastructure.

Recognizing Japanese Knotweed

This plant forms clumps called colonies or clones. At maturity, towards the end of July, a colony measures between 1 and 3 metres in height. Leaves are oval to triangular. They have pointed tips and truncated bases. Flowers are creamy-white and clustered. Flowering takes place in August and September.

Preventing the spread of Japanese knotweed

Although Japanese knotweed can produce viable seeds, it spreads mainly vegetatively. Small fragments of rhizomes or stems can produce new plants.

Several vectors contribute to the dispersal of fragments, including:

  • machinery and equipment contaminated with soil containing plant fragments,
  • excavation work involving soil transport,
  • bank erosion by water and ice.

Given the harmful effects of Japanese knotweed on the environment, and because it is very difficult to eradicate once established, it is important to prevent its spread by avoiding multiplying, transporting or dispersing it.

Collection of Japanese knotweed clippings

Sutton residents who cut Japanese knotweed on their property can contact the Town to have the residue collected and sent to an engineered landfill site, so as to limit the spread of this invasive plant.

To schedule a collection, write to [email protected], indicating where the colony was cut and how many bags will be collected. Japanese knotweed clippings must be placed in a sturdy, well-sealed plastic garbage bag. Place the bags at the curb on the day of garbage collection, on the date agreed with the designated employee.

  • Do not pile them on an unaffected section of land, on the edge of or in a watercourse or ditch.
    • Avoid putting parts of Japanese knotweed or any other invasive exotic plants in the brown bin dedicated to composting: as Japanese knotweed is a very tolerant species, the temperature generated by the composting process cannot guarantee the destruction of the plant and its rhizomes.
  • Clean any equipment that has been in contact with the plant to avoid dispersing stem and rhizome fragments or seeds when moving machinery or transporting soil. Avoid using this soil.
  • Plant fast-growing, competitive plant species where soil has been exposed.

Monitoring colonies on Sutton’s territory

If you observe Japanese knotweed along a public road or on public land, please write to us at [email protected] with photos and location.

Japanese knotweed eradication methods

Pour en savoir plus sur les méthodes d’éradication de la renouée du Japon, consultez :

Source: MELCC,