Japanese knotweed is a tall shrub with bamboo-like stems. It has been planted throughout South and Central Vancouver Island and the Gulf Islands as a garden ornamental but quickly spreads to form dense thickets in a variety of habitats, including dry roadsides and moist stream banks. Small patches can quickly spread into large areas, leaving little room for native species to grow.
These plants can be identified by their tall (>3 metres), bamboo-like stem structure, leaves that are flat at the base with a pointed tip and small white flowers that bloom in late summer.
Family: Polygonaceae (Buckwheat).
Other Scientific Names: Fallopia japonica, Reynoutria japonica, Polygonum cuspidatum.
Other Common Names: Asian knotweed, donkey rhubarb.
Growth Form / Reproduction: Deciduous perennial. Spread mainly vegetatively from rhizomes but will produce viable seed if Bohemian knotweed is nearby.
Legal Status: Forest and Range Practices Act, Community Charters Act.
Agricultural: Knotweeds can be eaten by grazing animals.
Ecological: Dense stands may compete with and replace native vegetation.
Human: Knotweeds have been used as landscape ornamentals.
Habitat: Adapted to moist conditions and to a variety of soil types; generally shade intolerant. Disturbed sites, roadsides, streams banks, ditches, wetlands, riparian areas, railroad and utility corridors
Status and Distribution: Widespread in all Regional Districts except Capital where it is common. Most common in CDFmm, CWHxm and CWHvm but present in CWHvh and CWHdm.
Management Strategy: Eradicate new infestation where feasible. Contain or control existing populations. Once established, knotweeds are extremely difficult to control; the rhizomes extend meters beyond the clones and they can regenerate from tiny fragments. Digging or hand-pulling can result in plants re-sprouting. Cutting, mowing, grazing and foliar herbicides can reduce top growth but repeated treatments are required for long-term control.
For more information on how to manage knotweed on your property and how we can help, visit our other page on Knotweed Management.
Invasive Plant Council of BC – Knotweed
Invasive Plants of Southwestern BC: Japanese Knotweed
BC Government Information on Invasive Plants
Understanding & Controlling Invasive Knotweeds in BC by Jeff Hallworth
King County, USA, Best Management Practices for Knotweed