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Knotweeds

Family Name
Polygonaceae
Species
Fallopia japonica, F. sachalinensis, Polygonum polystachyum
Classification
Invasive

Knotweeds, also known as “ornamental bamboo,” were introduced as ornamentals from eastern Asia. Knotweeds are vigorous, adaptable plants with densely leafy, bamboo-like stems that grow from extensive, often deeply rooted rhizomes. Growing 2 to 5 m high, these aggressive perennials have feathery, white to pink flowers with significant seed production potential.

How does it spread?

Knotweeds reproduce by vigorous creeping rhizomes, seeds and root fragments. Even very small pieces of the roots or rhizomes can produce new plants in remarkably little time. Overwintering rhizomes can remain dormant for years but once stimulated, will rapidly extend both outward and deep into the soil. Seeds are wind-blown and can be spread by water and human activites.

Where would I find it?

Invasive knotweeds are found throughout coastal areas of the province, the southern Interior and the northwest. Knotweeds tolerate partial shade but grow best in warm climates with full sun, in moist, rich, disturbed soil. They are common in exposed habitats such as along watercourses, in gardens, drainage areas, roadsides, beaches, parks and field edges. They can easily grow through cracks in wood, concrete and asphalt.

What problems does it cause?

Knotweeds are among the most difficult plants to eradicate from the landscape, as both seeds and rhizome fragments can start new plants. They shade out other vegetation, increase soil erosion potential and degrade habitat. They also easily penetrate and damage roads, buildings and drainage infrastructure. Infestations can reduce sight lines along roads, fences and rights-of-ways and impact water recreation access and activities, threaten safety and decrease amenity values.

Additional Recommendations

  • Oceanspray (Holodiscus discolor) BC native (z6)
  • Sasktoon berry (Amelanchier alnifolia) BC native (z3/4)
  • Fothergilla (Fothergilla major) (z5)
  • Heavenly Bamboo (Nadina domestica) (z7)

A provincial initiative coordinated by ISCBC

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