Japanese Knotweed Japanese Knotweed is one of four knotweed species found in B.C. Native to Asia, it was introduced to BC in the early 1900s as an ornamental plant. It immediately appealed to landscapers because it was attractive and fast growing. Unfortunately, as well as being fast growing, it is also very difficult to eradicate and these two characteristics earned knotweed a place on the B.C. Invasive Species List. According to the BC government, Japanese Knotweed falls in the category of a “Species that is high risk and well established, or medium risk with high potential for spread. The Management objective is to prevent further expansion into new areas within the region through establishment of containment lines and identification of occurrences outside the line to control.” Japanese Knotweed thrives in moist soil and can be found in riparian areas, wetlands and even areas prone to seasonal flooding. It can tolerate a variety of soil conditions including those with heavy metals and salt. It prefers sunny locations but can still flourish in part shade. You will find it along forest edges, on derelict land, beside roads, and along railway right-of-ways Japanese Knotweed's ability to grow in a variety of soil types and its preference for moist, sunny conditions contribute to its widespread distribution throughout B.C. Within B.C. Japanese Knotweed is more predominant in coastal areas such as Vancouver Island, the Sunshine Coast and the Lower Mainland. In appearance, a mature Japanese Knotweed has hollow, jointed stems that are purple to green in colour and up to 2.5 cm in diameter. The bright green leaves are 10-17 cm long and 7-10 cm wide and somewhat oval or heart-shaped with a pointed tip. They grow on alternate sides of the long stalk in a distinctive zigzag pattern. In late July or early August small white-green flowers bloom in clusters at the ends of the stems or where the leaf joins the stalk. And the roots? Well, technically they are rhizomes. A rhizome is actually a stem with sections and nodes; each node is capable of producing new shoots and roots. Think of a ginger root but larger and the branching structures are woody and have a tough, dark brown outer layer and a distinct orange interior. As rhizomes grow and spread they develop into clumps called crowns that can grow up to 7 metres (23 feet) horizontally, penetrate as deep as 3 meters and regenerate from fragments as small as 0.7g. How amazing is this plant! It can multiply underground without flowering, survive extreme weather and soil conditions and regrow from the smallest fragment. Japanese Knotweed goes through a yearly cycle which includes: -a winter dormancy when the plant depends on the stored energy in its underground rhizome system in order to survive harsh weather. -early spring growth when new shoots appear that look like purple asparagus spears. -leaf development when the bright green heart-shaped leaves unfurl in a zigzag pattern along the reddish stems. -rapid summer growth when the stems can grow 8cm daily and the plant can grow 1 m. in height in three weeks. -late summer flowering when clusters of small creamy white flowers appear. -seed development which follows flowering when the plant produces small winged seeds -autumn decline when the above ground foliage turns yellow, then brown and finally dies back. But, underneath the ground the rhizome system is alive and able to sustain the plant until spring arrives again. Japanese Knotweed is dioecious, meaning there are separate male and female plants. It can reproduce through pollination and the standard process; bees are attracted to its flowers, pollen is transferred and seed are produced. However, when trying to control this plant’s rapid growth it is necessary to understand that Japanese Knotweed primarily reproduces vegetatively (not by seed). New plants are developed from the rhizome and also from small stem and root fragments. How can you get rid of Knotweed? You can start by clicking on this link and reporting your knotweed problem to: Coastal Invasive Species Committee (Coastal ISC). Also, here is a link to a CISC fact sheet: https://bcinvasives.ca/wp-content/uploads/2021/01/ISCBC-Factsheet-Knotweeds-180216-WEB.pdf One local resident, with a knotweed problem wrote to us with their experience: "One lead I have had is with the Coastal Invasive Species Committee (Coastal ISC). They are based on the big island in Colwood, but do come to the Sunshine Coast one or two times per year to treat some areas. They offered to treat our Knotweed for what I thought was a reasonable price. The problem is that our Knotweed is right inside a drainage ditch, .... and they don't want to use any chemicals when water is running, which makes sense.  But both times they've come to our property, there's been water in the ditch, and they've left without doing any work. I've tried engaging them regarding the 2025 schedule, but when they finally did answer they advised that they are fully booked for the year. I did check some local landscapers for private service. The hard part is fully eradicating the weed. That's fine - I would be happy with a reduction and control for now. It's far enough away from our actual home that ongoing control would be just fine in my books." And so, what is the impact of this plant? There are definitely negative aspects. As an invasive plant, Japanese Knotweed can outcompete local vegetation, disrupt the food chain and reduce biodiversity. It can also damage infrastructure like roads, railways, and building foundations by pushing through cracks in asphalt, concrete, and other materials. It appears that Coastal ICS is not fully responsive to this challenge. But, there are positive aspects. For example, Japanese Knotweed is edible… the tender stems can be eaten raw or cooked and are reported to taste much like rhubarb. Consequently, it can be used as a rhubarb substitute for crumbles, pies, sorbets, sauces, pickling, and in beer, wine and herbal teas. It’s somewhat of a surprise…but, yes, Japanese Knotweed has been featured in Bon Appetit. Another positive aspect relates to health. Japanese Knotweed has been used in Traditional Chinese Medicine for centuries to treat certain types of viral infections. Despite a variety of claims for some of today’s most worrisome health disorders, the claims made on behalf of Japanese Knotweed have yet to be proven by strong scientific evidence. Perhaps the most important positive contributions of Japanese Knotweed are yet to be discovered. In the meantime we are left to find ways to keep it in check as best we can until more government attention to this invasive plant materializes.