Invasive Plant

Himalayan Knotweed

Koenigia polystachya
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Warning

All knotweeds species in BC can grow through concrete and asphalt, damaging infrastructure. This can results in significant control, management, and repair costs.

About This Species

Knotweeds were introduced to British Columbia for use in gardens and landscaping due to their rapid growth and attractive appearance There are now four species established in BC: Bohemian, Giant, Himalayan, and Japanese knotweed. Knotweeds grow aggressively and are very hard to kill. They are widespread throughout the province, and are often found in riparian areas, , derelict land, road and railway right of ways and gardens. They thrive in moist soil and full or partial sun. Knotweeds can spread by seed, root fragments, and stem fragments, making them very difficult to control. Knotweeds are considered noxious weeds in BC.

How to Identify

Knotweeds have attractive plumes of small, white to green
flowers in the spring. Himalayan knotweeds, unlike the other three species, have elongated, tapered leaves that are 8-10 cm wide and 15 cm in length. Similar to bamboo canes, stems grow tall, straight and densely (at a rapid pace). They are hollow and green, sometimes with reddish-brown speckles, and up 5 m in height. Stems may persist through the winter as bare, grey- or straw-coloured hollow stalks.

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A few non-invasive alternatives to plant instead of Himalayan Knotweed include:

  • Red-osier dogwood (Cornus stolonifera)
  • Black elderberry (Sambucus racemosa var. melanocarpa)
  • Pee Gee hydrangea (Hydrangea paniculata ‘Grandiflora’)
  • False Solomon’s-seal (Maianthemum (Smilacina) racemosum subsp. amplexicaule)
  • Goat’s beard (Aruncus dioicus)

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