Originally populating the volcanic slopes of eastern Asia, it’s no wonder this invasive is a pro at busting through the concrete and asphalt of house foundations and roads.
I’m a plant that’s invasive beyond belief,
Able to grow through concrete, good grief!
I grow on stream banks and form dense strands,
I cause erosion to much of the land.
Japanese Knotweed (Fallopia japonica/Reynoutria japonica) is an aggressive perennial, easily identifiable by its leaf shape and size. A bamboo-like hollow green stem with red speckles is characteristic of all 4 varieties of knotweed: Japanese Knotweed, Bohemian Knotweed, Himalayan Knotweed, and Giant Knotweed. Three of those have been reported growing in the Sea to Sky region, Giant Knotweed being the exception.
Another shared characteristic among the 4 knotweed species is the plume-like, branched flower clusters that bloom in late summer. Because of these flowers, knotweed is sometimes mistaken for Ocean Spray, a native species, differentiated by its coarsely-toothed, lobed leaves.
Knotweed species are differenciated by their leaf shape and size. Indeed, Japanese Knotweed’s egg-shaped, 3-10cm long leaves set it apart from its close relatives, all with significantly larger leaves with hairy undersides.
Since its introduction to British Columbia in the 1900s, Japanese Knotweed has rampantly spread through the coast, dominating rivers, creeks, ditches and other areas offering moist soil and good sunlight. The perfect mix of high reproductive capacity and lack of natural predators makes Japanese Knotweed a tough invasive to control.
Knotweed’s high reproductive capacity is due to its ability to spread rapidly, thanks to its root system and its ability to sprout new plants from small pieces of stem or root tissue (as little as 0.7 grams!).
Japanese Knotweed’s astounding ability for vegetative reproduction is the real kicker when it comes to controlling this harmful invasive. Unlike most other invasives in the Sea to Sky, mechanical control methods, such as mowing or hand pulling are NOT recommended. Please refer to the Metro Vancouver Best Management Practices document to learn more about how to control knotweeds, or contact SSISC to discuss site-specific requirements.
As the SSISC Priority Species list states, our goal is to contain Japanese Knotweed within the south of the Sea to Sky region and work on eradicating infestations in the Whistler and Pemberton areas. If you suspect you have come across any type of knotweed, please report your sighting here.
I Spy in the Sea to Sky Contest
Guess the invasive species in our I Spy in the Sea to Sky weekly social media post, July through August, to enter the giveaway. At the end of each month, one lucky commenter will win a Native Wildflower seed mix packet!
Contest Rules:
- Comment your guess (common/species name) on either Facebook or Instagram post to enter
- One entry per person per post
- Anyone can play, but only residents of the Sea to Sky region are eligible to win (as prizes will be delivered)
- Content entries will close at 11:59 PM PST on the last day of the month
- Winners will be announced in the first week of the following month on the SSISC Instagram story and contacted via their platform of entry
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