Invasive Plant

Japanese Knotweed

Reynoutria japonica
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Warning

All knotweeds species in BC can grow through concrete and asphalt, damaging infrastructure. This can result 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, stockpiled material (example: soil, aggregate, mulch), 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 a noxious weed in BC.

How to Identify

Knotweeds have attractive plumes of small, white to green
flowers in the spring. Leaves are heart- to triangular-shaped, 8-10 cm wide and 15 cm in length. A distinguishing feature of Japanese knotweed is that its leaves grow in a zigzag pattern in along the plant’s arching stems. Similar to bamboo canes, stems grow tall, straight and densely (at a rapid pace). They are hollow and green, sometimes with reddish-brown speckles growing 1 – 5 m in height. Stems may persist through the winter as bare, grey- or straw-colored hollow stalks.

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A few non-invasive alternatives to plant instead of Japanese 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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