Japanese Knotweed shoots, leaves, flowers and seedlings
Japanese Knotweed can be difficult to identify due to its changing appearance through the seasons. Take a look below to find out how you can spot this pernicious weed all year round and what to do once you’ve found it.
How quickly does knotweed spread?
Japanese Knotweed is the UK’s fastest-growing invasive weed. Its peak growing period is in the summer when the pesky plant can grow up to 100 mm per day and reach heights of more than seven metres.
If left untreated, Japanese Knotweed can quickly spread, and those innocuous little shoots will soon become a garden menace. It will quickly overwhelm other garden plants and spread into neighbouring gardens which can potentially result in a fine or even an ASBO.
Why is Japanese Knotweed a problem?
As one of the UK’s worst invasive species, Japanese Knotweed has been a horticultural horror for homeowners, businesses, and local authorities alike for years, costing thousands of pounds in damages every year.
Japanese Knotweed is a robust, voracious plant able to grow in the most inhospitable of environments and survive the harshest conditions. In Japan, it can be found growing on the rocky slopes of volcanoes, which makes it incredible tenacious and easily able to thrive in our more clement UK climate.
Even in our more rocky, built-up areas, it is able to exploit cracks and fissures in brick walls and concrete as it seeks out water and light, causing costly structural damage in the process. It can also send down roots up to three meters underground, making it difficult to get rid of, since any residual rhizomes (as small as 2 mm) can cause a regrowth.
How can you get rid of Japanese knotweed?
While it is possible to remove Japanese Knotweed yourself, it is a long and difficult process. There are herbicides available for the public to use, but as a professional removal company we are permitted to use stronger industry specific products which are more powerful and can do the job faster. Our methods include spray herbicides and stem injection herbicides.
Another means of removing Japanese Knotweed is excavation. This is a faster method, but also a more costly one, and since soil containing Japanese Knotweed is classified as controlled waste in the UK, you will need to have the soil sifted and screened.
If you suspect you or a neighbour has Japanese Knotweed, you can see some plants that look like Japanese Knotweed here. For further information on Japanese Knotweed or any of our removal techniques, please contact Japanese Knotweed Specialists or give us a call on 0800 122 3326
Can you burn Japanese knotweed?
Before burning Japanese Knotweed, you need to ensure it is thoroughly dried it out; only then can it be incinerated with no chance of regrowth. However, we recommend using a professional service, such as our own; Japanese Knotweed Specialists use the Burnwell micro incinerator, supplied by Kingwell Holdings, a mobile burner which is easy on the environment, and produces less noise and dust.
What type of plant is Japanese knotweed?
Japanese Knotweed, Fallopia japonica, also known as Asian Knotweed, is a herbaceous perennial plant of the knotweed and buckwheat family Polygonaceae. Although native to Japan, it was brought to Europe in 1850, and praised as an exotic botanical wonder; since then, it has gone on to be classified as one of the UK’s most invasive species of plant.
Japanese Knotweed through the seasons
Japanese Knotweed changes in appearance through the seasons, which can make it difficult to identify. If you do suspect an unwelcome garden visitor, you can send Japanese Knotweed Specialists a photo, and we’ll identify it for free with no obligation. So what does Japanese Knotweed look like during the different seasons?
Japanese Knotweed in the spring
Spring is the prime growing season for Japanese Knotweed. You’ll notice new red or purple shoots, a little like asparagus spears, sprouting up, while its reddy or dark greenish leaves will still be rolled up. The canes will begin growing by late spring and could reach up to a couple of metres already.
Japanese Knotweed in summer
The leaves of Japanese Knotweed will be fully open by now; you’ll recognise them by their distinctive shovel/heart shape. Later in the summer, small clusters of white flowers will appear. The stems may seem similar to those of bamboo, and you’ll notice the leaves grow in an alternating pattern along the stem.
Japanese Knotweed in autumn
Japanese Knotweed maintains its thin foliage in autumn but its leaves will start to turn yellow and wilt towards the end of the season. You’ll also notice the stems starting to turn brown.
Japanese Knotweed in winter
Japanese Knotweed will lose its leaves during the winter and the hollow bamboo-like stems will die off and fall in on each other as the plant becomes dormant.
Japanese Knotweed leaves
One of the easiest ways to identify Japanese Knotweed is through its tell-tale heart-shaped or spade-shaped leaves which grow into a point. The luscious green leaves grow in an alternating pattern along the stem and can reach about 200 mm in length.
Japanese knotweed flowers
Japanese Knotweed flowers will start sprouting towards the end of August, in elongated clusters of about 5mm wide and 100mm long.
What colour are the flowers of Japanese knotweed?
The flowers of Japanese Knotweed are a creamy white colour.
Japanese Knotweed rhizome
What are rhizomes? Rhizomes are like stems that grow underground. Japanese Knotweed rhizomes can grow down to a depth of three metres and extend outwards up to seven metres. Japanese Knotweed normally spreads via its rhizomes; a fragment as small as 0.7 grams of viable rhizome is enough to give rise to a new plant.
Are Japanese Knotweed stems hollow?
Yes, the stems of Japanese Knotweed are hollow, and look like bamboo stems with clearly defined rings or nodes and purple speckles. They are reddish green in colour, and when mature will reach up to two or even three metres in height. The stems of Japanese Knotweed aren’t at all woody and can be snapped relatively easily.
How does the knotweed reproduce?
Japanese Knotweed does produce seeds, but it is very rare for these seeds to germinate and spread. The most common means by which Japanese Knotweed spreads is via fragments of stem being transported in contaminated soil or water. Strimmers, flails and mechanical cutters can unintentionally spread Japanese Knotweed.
Can Japanese knotweed spread by seed?
Although, it is possible for Japanese Knotweed to spread via seeds, it is very uncommon, and the plant usually spreads via fragments of rhizomes being transported in contaminated soil.
Images of Japanese Knotweed
See our full gallery of Japanese Knotweed.