What is Japanese Knotweed?
Japanese knotweed is a highly aggressive weed that can cause damage to property. With bamboo like stems and small white flowers, knot weed can grow up to 10cm per day. The nasty weed finds weak points and masonry cracks to grow through which can cause major damage to buildings.
How Did Japanese Knotweed Get Here?
Native to Japan, Korea and parts of East Asia and China, Japanese Knotweed was brought to the UK by a German-born botanist, Philipp von Siebold in 1850, on the wave of popularity surging through Victorian Britain to collect and study plants from across the world. Japanese knotweed flowers and foliage were used for animal fodder and, at first, prized for their beauty—so much so, that in 1847, the species was named as ‘the most interesting new ornamental plant of the year,’ by the Society of Agriculture and Horticulture in Utrecht.
Inevitably, the interest in Japanese Knotweed quickly evolved into, ‘How on earth can we get rid of the stuff?’ because it proved to be a ferocious, invasive and destructive plant. In its natural habitat, on the side of volcanoes, the extreme climate, deposits of volcanic ash, native fungi and insects limited its spread, but in Britain there are no such natural regulators or predators.
What Does Japanese Knotweed do?
Japanese Knotweed costs the UK economy an estimated £166 million per year for treatment and in property devaluations.
It spreads—rapidly—and it wipes out native species in its relentless progress across the land, as well as posing a serious threat to building foundations and drains. At its most prolific, Japanese Knotweed can grow 20 cms in a day; its root system can go down to 3m; one plant can extend as much as 7m in every direction and it can break through tarmac and concrete.
So, Japanese Knotweed spreads like wildfire when it’s growing, but it also spreads when anyone tries to get rid of it, unless professionally managed by companies such as ours—Japanese Knotweed Specialists. The tiniest fragment of stem or rhizome will easily take root and regrow into another voracious plant so it’s a real demon to eradicate.
In Victorian times, the gardens of the aristocracy were crammed with exotic plant species, and should one fail to thrive or simply go out of vogue, it would be dug up and discarded. Japanese Knotweed was one such plant, dumped in disused quarries, waterways or anywhere conveniently out of sight. This practice continued, unknowingly exacerbated by the movement of contaminated soil for road and railway-building and construction projects, until the full extent of the damage it caused became apparent.
Yes, Japanese Knotweed thrives, anywhere and everywhere. It will continue to thrive, given half a chance, despite recent legislation strictly controlling the transportation and disposal of stems, roots and infected soil.
Find out more about Japanese Knotweed legislation here.
What Does Japanese Knotweed Look Like?
The plant has many guises, depending on the time of the year. Our seasonal Japanese Knotweed pictures will allow you to understand what you’re looking for.
Read our guide on plants that look like Japanese Knotweed including Bindweed, Himalayan Balsam, Bamboo, Russian Vine and more.
Japanese Knotweed Through the Seasons
Japanese knotweed in spring:
- The first signs of Japanese Knotweed growth, Usually the early signs of growth are seen in mid-March
- Distinctive red and purple shoots – often accompanied by rolled back leaves which grow rapidly from the stored nutrients in the rhizome.
Japanese knotweed in summer:
- The stem resembles bamboo, though more green in colour with purple speckles.
- Inside the cane are distinctive chambers that retain water and nutrients.
- The leaves are large and have pointed tips that extend from the stem in a zig-zag pattern.
- Later in the season creamy-white flowers hang in clusters from the stalks.
Japanese knotweed in autumn:
- The plant will have dense hollow bamboo stems turning a darker brown with a lot of foliage.
- The leaves are large and have a heart shape with pointed tips that extends from the stem in a zig-zag pattern.
- The leaves will be wilting and beginning to turn yellow.
Japanese knotweed in winter:
- As the first frosts appear the plants leaves will turn brown and the plant withdraws back into its rhizome.
- The canes lose their colour and turn into woody stalks which can take years to decompose.
- New shoots can be found growing through the dead canes in the early Spring.
Japanese Knotweed Identification Made Easy!
Although, please note that there are other plants mistaken for Japanese Knotweed, including:
- Russian Vine
- Himalayan Honeysuckle
- Persicaria Microcephala
- Houttuynia Cordata
Read our guide on PLANTS THAT LOOK LIKE JAPANESE KNOTWEED.
Use our upload files facility below to send us photographs of the plant you suspect is Japanese Knotweed and we’ll check them out for you.
What Should You do if You Find Japanese Knotweed?
First of all, make sure it really is Japanese Knotweed, by referring to our Japanese knotweed images or by sending us some photographs below.
If the issue is minor, we may suggest some less invasive methods of killing Japanese knotweed before you’re forced to bring in a team of professionals.
As Japanese Knotweed contractors and consultants we are here to help, anywhere in the UK.
With a number of different removal and treatment options available, please call our specialist knotweed removal team on 0800 122 3326 for advice.