Infamous for its devastating ability to cause costly damage to property, Japanese knotweed is the most widespread form of knotweed in the UK. Typically blooming between late summer and early autumn, Japanese knotweed flowers are a distinct creamy white colour and form in clusters of up to 10cm long. Dying back around October, the flowers leave behind hollow stems throughout the winter months.
On this page, we’ll look at how to identify Japanese knotweed, characteristics of Japanese knotweed, different types of Japanese knotweed, plants that look like Japanese knotweed and many other Japanese knotweed related topics and subtopics.
How to identify Japanese Knotweed?
Frequently mistaken for common shrubs such as dogwood due to the large amounts of foliage it produces, Japanese Knotweed is identified by its creamy white flowers, bamboo-like stems and shovel-shaped green leaves. Below we’ve created a detailed overview of Japanese Knotweed characteristics.
Japanese knotweed characteristics
- Japanese Knotweed Flowers – Cream white colour, 0.5cm wide, forms clustered panicles that can grow to 10cm. Blooms very late summer (August/September)
- Japanese Knotweed Height – Typically grows to 2.1m (7ft) but can grow up to 3m (9.8ft).
- Japanese Knotweed Leaves – Light green with red or purple flecks. Heart or shovel-shaped with a pointed tip and shoot out from nodes in a zig-zag pattern. New Japanese Knotweed leaves are rolled up with dark red veins while mature leaves can grow up to 20cm.
- Japanese Knotweed Stem – Grows in a zig-zag pattern, green with purple and red speckles, hollow and grows to 2-3 metres in height. Can Grow up to 2cm a day.
- Japanese Knotweed Roots (Rhizomes) – Outside is dark brown, inside is orange/yellow. Can grow 3 metres deep and between 2 to 7 metres horizontally, depending on soil and weather conditions. The diameter is approximately 20cm.
- Japanese Knotweed Growth Rate – Can grow up to 10cm per day during late spring / early summer.
- Japanese Knotweed Seeds – Heart-shaped and feature small wings. Extremely rare for seeds to germinate. New plants grow from nodes or pieces of green stem in soil or water.
- Japanese Knotweed Species – Reynoutria japonica from the Polygonaceae family.
- Japanese Knotweed Order – Caryophyllales
- Japanese Knotweed Origin – Native to Japan, China and parts of Korea and Taiwan.
Japanese knotweed is a hotly debated topic in Parliament , within the property industry and in the courts, however, positive identification of the plant is required before any legal action is started. Although the plant has a few defining features (broad green, shield-shaped leaves and bamboo-like stems), Japanese knotweed takes on different forms throughout the seasons. Therefore, if you know what you’re looking for, it’s possible to discover an infestation at any point in the year.
Correctly identifying Japanese knotweed requires a keen eye and some key pieces of information. The plant does have some unique characteristics, however, it can also be confused with a number of other plants, which can make isolating an infestation difficult. By assessing each component of the suspected plant you can discover if you’ve found Japanese knotweed on your land or not.
This guide is intended to point property owners in the right direction when it comes to identifying this invasive plant and takes into account how knotweed appears throughout the year, other plants that it’s often mistaken for and what risk factors are related to an infestation.
What Does Japanese Knotweed Look Like?
Japanese knotweed flowers are often described as ‘creamy white’  and appear towards the end of summer, from late August to September. Growing in clusters up to 10cm long, they appear alongside the bright green leaves, combining to create a large vegetative mass. Related species of Japanese knotweed can be adorned with similar clusters of flowers in shades of pink and red.
Japanese knotweed can be recognised by its red stems when it first emerges in spring, however, this colouration does not remain consistent throughout its lifespan. As the plant matures, the stem takes on a less distinctive green colour with mauve spots. It should be noted that these stems look like canes, growing in clearly defined segments with a hollow centre, similar to that of bamboo.
When the plant is in foliage, Japanese knotweed leaves are bright green and feature a signature shield or heart-shaped leaf. Each leaf has a pointed end and is arranged at staggered intervals along the stem. Leaves can be up to 14cm long, but don’t expect to see any during the winter, as the plant’s green foliage doesn’t last through the colder months.
Japanese knotweed (Reynoutria japonica/Fallopia japonica) is the most common species of the plant found in the UK , however, it has been known to hybridise with related species. Giant knotweed (Fallopia sachalinensis/Reynoutria sachalinensis) is found widespread throughout the UK but is not as common as Japanese knotweed . Fallopia japonica var. ‘Compacta’ is the dwarf variety of the plant, that is much smaller in stature.
Fallopia x bohemica or Reynoutria x bohemica is the result of a hybridisation between Fallopia japonica and Fallopia sachalinensis, it tends to grow larger than Japanese knotweed . Hybridisation has also occurred between the closely related Russian Vine (Fallopia baldschuanica), its common name is railway-yard knotweed.
Japanese knotweed can typically be identified during early summer by its hollow stems that feature purple speckles and are up to 3 metres in height. The less frequently occurring Giant knotweed can grow up to 5 metres in height, whereas the hybrid Fallopia x bohemica has been known to grow up to 4 metres. Dwarf knotweed does not typically exceed 1 metre in height.
Japanese knotweed has heart-shaped seeds that feature small wings. New growth from seeds is very rare , as only the female of the species was imported into the UK. For the most part, Japanese knotweed has been spread throughout the country by the transportation or fragmentation of its rhizomes. The rhizomes are effectively the plant’s root systems, with a fragment of the rhizome capable of generating an entirely new plant if given the proper conditions. Unfortunately, Japanese knotweed has been observed to hybridise with other related species  which has led to new plants that are able to then spread by seed down the line.
Different Types of Knotweed
There are four main different types of Japanese Knotweed. These are: Giant Knotweed (Reynoutria sachalinensis, formally Fallopia sachalinensis), Himalayan Knotweed (Persicaria Wallichii), Dwarf Japanese Knotweed (Reynoutria Japonica var. ‘Compacta’, formally Fallopia Japonica var.
When is the Best Time to Identify Japanese Knotweed?
The best time to identify Japanese knotweed is mid-late summer. At this time of year, the plant is in full growth and canes should be around 2m tall. Not only will the height of the canes make the plant conspicuous, but the plant’s leaves will also be at their most abundant. Large masses of lush green, spade-shaped leaves make Japanese knotweed easy to identify at this time of year. Unsurprisingly, summer is when the majority of infestations are reported as homeowners are spending more time outdoors and are more likely to notice the advanced growth of Japanese knotweed on their land.
Towards the end of summer, Japanese knotweed flowers provide another means to easily identify an infestation. Summer is also an ideal time of year to start a treatment plan. Leaves are constantly absorbing nutrients for storage throughout the winter, so when Glyphosate is painted onto leaves, the herbicide is quickly absorbed down into the plant’s rhizomes for maximum effectiveness.
Japanese Knotweed in Spring
Japanese Knotweed grows fastest during the spring. In spring, Japanese Knotweed’s springs new shoots that emerge as red/purple asparagus-like spears. Knotweed leaves are normally dark green or red and rolled up during this time of the year. In late spring, Japanese Knotweed canes can reach up to 3 meres in height.
The plant can be difficult to spot until major growth above the surface begins to take place. Early spring is usually when the first Japanese knotweed shoots begin to appear, usually at the base of old canes (in the case of patches that are more than a season old). Knotweed shoots can be spotted by their bright red or pink tips. These pinkish redbuds grow to be around 1-3cm wide but do not keep this distinctive colour for long.
Once spring is well and truly underway, shoots take on a greener hue and become easier to spot due to their accelerated growth . Now growing as spear-shaped shoots, sometimes described as ‘asparagus-like, the leaves are red and rolled up, but they soon turn green as the plant grows skyward.
Japanese Knotweed in Summer
In the summer, Japanese knotweed is easier to spot as its spade-like pointed leaves are bright green, this is when the plant is most visible above ground. Knotweed growth accelerates significantly during summer, making the plant much more conspicuous. Japanese Knotweed hollow stems grow up to 2cm a day and in the summer the leaves now are most easily recognised by their shield shape with an alternating stem pattern. This presents a good opportunity to treat the problem with a PCA-accredited glyphosate programme , professionals are able to assess an infestation and inject each plant with their specialist equipment.
Related: How To Get Rid Of Japanese Knotweed
By mid-summer knotweed plants are close to reaching their full height (between 1.9-3m). The stems are now less green and are rigid with more pronounced dark purple speckles. Clear nodes are visible on these stems giving them the appearance of bamboo, they can also be snapped easily in the hand. It’s not until late summer that Japanese knotweed flowers; multiple bunches of creamy white flowers appear amidst the leaves, but the seeds that are produced from this process rarely lead to new growths.
Japanese Knotweed in Autumn
As autumn progresses, the characteristically bright green leaves turn a vivid yellow and the plant sheds seed cases. If the weed is left to its own devices the leaves and flowers will eventually begin to fade and fall back. Leaves fall off the stems which start turning brown and then a pale straw colour as winter progresses, also taking on a more rigid, woody form.
Japanese Knotweed in Winter
Knotweed appears to ‘die back’ during winter, but it’s unwise to assume that the problem is simply gone. In the middle of winter, all that remains above ground is a collection of pale, dry canes with the Japanese knotweed dormant beneath the surface waiting for warm weather to sprout and spread further. Whilst the plant enters this dormant phase it is still very much alive.
Japanese knotweed leaves are heart-shaped with a pointed tip, some also describe them as shovel or spade-shaped . Each leaf is staggered on the stem, forming a zig-zag growth pattern which gives the plant maximum opportunity for soaking up sunlight. Leaves are a lush green colour and grow up to 20cm long. One plant can feature dozens of these leaves which are perfectly designed to deliver energy to the plant’s rhizome system and encourage more growth at a later time.
When trying to differentiate Japanese knotweed leaves and Hybrid knotweed leaves, take a close look at the edges. Hybrid plants tend to have crinkled edges, whereas the original plant’s are smooth. Japanese knotweed leaves also tend to be a lighter shade of green and have a broader base (which some describe as more shield-like), whereas hybrid leaves have a more accentuated heart-shaped profile. You may also notice fine trichomes or hairs on the underside of hybrid leaves whilst Japanese knotweed are hairless underneath .
Japanese Knotweed Flowers
Japanese Knotweed flowers are identified by their creamy-white coloured panicles forming in late summer as clusters that grow up to 10cm long. Knotweed flowers develop between the end of August and early September . The flowers grow alongside the leaf foliage, creating a dense appearance that often blocks the trademark stems from view. Each individual flower, from within the cluster, is small in size. A flowering Japanese knotweed plant is a sign that it is well established and could therefore be a challenge to remove. Identifying and treating the plant before it reaches the flowering stage in late summer can prevent a longer-term infestation.
Japanese knotweed flowers are mostly ornamental in nature as, in the UK, there is no male of the species to reproduce with. This doesn’t rule out potential hybridisation, however, as since the plant was introduced to the UK it has successfully hybridised with a number of native plants that are closely related to it. Japanese knotweed flowers have also been proven to be of use to beekeepers. Knotweed flowers arrive late in summer, compared to other flowering plants, which means that bees are given a last-minute alternate source of nectar to make honey with. Honey produced from the nectar from knotweed flowers is said to be similar to that of buckwheat honey .
Japanese knotweed roots are comprised of a network of rhizomes. These tough, woody roots can be collected together in large crowns which can be difficult to remove from the ground without the help of machinery. Rhizomes are dark brown on the outside and orange on the inside, you can usually break them in your hands unless they have grown into a larger clump or ‘crown’ .
Rhizome root systems can burrow up to 3 metres deep into the ground with individual rhizomes growing up to 20cm thick, but this kind of growth only occurs if the plant is given the time and space to flourish. The veracity of this plant can make matters particularly difficult in disputes involving neighbours. Japanese knotweed spreads easily underground during the winter via its root system without even the most attentive of gardeners noticing. Only in the spring, when shoots begin to emerge, would the knotweed problem be visible above ground.
Japanese knotweed stems are often compared to bamboo , as they have a similar node-based construction and are hollow on the inside. They start life as a pink or red shoot that is not dissimilar to asparagus in appearance, these are edible at this point and have become popular with foragers in the UK. Once the plant grows it takes on a greenish hue, before developing a darker, muddier shade and purple speckles when it reaches maturity. At its mature height of 2-3 metres, it is no longer edible, and each stem can be snapped easily in the hand. During autumn these stems start to turn brown, before becoming even more brittle and pale in winter.
Japanese Knotweed Identification Video Guide
How to get rid of Japanese knotweed?
Getting rid of Japanese knotweed is no easy task. Requiring professional chemical treatment in order to be effectively removed, Japanese knotweed is a controlled waste material – making it difficult to dispose of. The most proven way to kill Japanese knotweed is with a professional-grade glyphosate treatment plan, this also needs to be administered by a PCA-accredited firm that can offer you a guarantee that will be trusted by potential buyers and mortgage lenders. For a comprehensive overview of eradicating Japanese knotweed, see our page on how to get rid of Japanese knotweed.
Plants mistaken for Japanese knotweed:
As Japansese knotweed experts with extensive industry experience, we’re aware that many homeowners often mistake Japanese knotweed for other plants. There are a variety of sub-species and cross-breeds of plants that look like Japanese knotweed. When a correct identification of Japanese knotweed can be the difference between getting a mortgage request accepted or rejected by a lender, it’s imperative that the right plant is identified. In some cases, homeowners may be alarmed by the sudden appearance of a shrub-like plant or climbing plant and may be under the false illusion that they have Japanese knotweed. It’s important to rule out all other possibilities before any time or money is spent on calling out professionals to treat the infestation.
The following plants share look like Japanese knotweed but have a few crucial differences which may help you confirm or rule out a positive identification of the plant:
Plants that look like Japanese knotweed:
Here’s a comprehensive list of plants that look like Japanese knotweed and are commonly mistaken for being Japanese Knotweed:
- Lesser Knotweed (Persicaria campanulata)
- Lilac and Woody Shrubs & Tress
- Giant Knotweed (Fallopia sachalinensis)
- Dwarf Knotweed (Fallopia japonica var. compacta)
- Fallopia x bohemica
- Railway-yard Knotweed (Fallopia x Conollyana)
- Russian Vine (Fallopia baldschuanica)
- Hedge Bindweed (Calystegia sepium)
- Dogwood (Cornus) and woody shrubs and Trees
- Heart-leaved houttuynia (Houttuynia cordata)
- Red Bistorts (Persicaria amplexicaulis)
- Himalayan Balsam (Impatiens glandulifera)
- Broadleaved Dock (Rumex obtusifolius)
- Himalayan Honeysuckle (Leycesteria formosa)
- Horsetail (Equisetum arvense)
- Buckwheat (Fagopyrum esculentum)
Lesser Knotweed (Persicaria campanulata)
Referred to by some as Polygonum polystachyum, Lesser Knotweed is frequently mistaken for Japanese knotweed. This is due to its similar bamboo-like hollow stems, small flower clusters and similar height. Native to the Himalayas, Lesser Knotweed is one of the least common knotweeds in the UK and differs from Japanese knotweed in its long thin ovate leaves, and pink flowers.
Similarly featuring green spade-shaped leaves, Lilac is commonly mistaken for Japanese Knotweed. Unlike Japanese knotweed, Lilac leaves grow opposite each other along woody stems. However, Lilac’s vibrant iridescent flowers – blooming in early spring – provide the clearest visual difference from Japanese knotweed.
Giant Knotweed (Fallopia sachalinensis)
Growing up to 5 metres in height, Giant knotweed (Reynoutria sachalinensis, formally Fallopia sachalinensis) is one of several different types of Japanese Knotweed . Other different types of Japanese Knotweed include dwarf Japanese Knotweed (Reynoutria Japonica var. ‘Compacta’, formally Fallopia Japonica var. and Himalayan Knotweed (Persicaria Wallichii).
Whilst Giant Knotweed plant is found throughout the UK, it’s not as commonly found as its smaller relatives. The plant was imported to the UK around the same time in the 19th century as a curiosity for Victorian horticulturists who were impressed by the speed of which this plant could grow. Similar to Japanese knotweed, it has spread mostly through the dispersion of its rhizomes as opposed to typical reproduction methods.
Dwarf Knotweed (Fallopia japonica var. compacta)
Considered to be much less invasive than Japanese knotweed, the dwarf variant grows to 1 metre tall at most and retains much of its larger relatives’ physical traits. The plants’ stems grow in nodes and stems are produced in a zig-zag pattern. The leaves are noticeably different, however, having a darker green hue and leathery appearance . The edges of the leaves are crinkles and feature reddish veins which can make it easier to distinguish from the lush green leaves of the more common species.
Fallopia x bohemica
Also known as Reynoutria x bohemica, this plant is a result of the hybridisation between Japanese knotweed and Giant knotweed . The plant grows in a similar fashion to Japanese knotweed however the leaves grow much longer than its relatives. Both sexes of the plant are found within the UK, with hermaphrodite plants outnumbering the sterile-male plants, however the plant still mostly spreads through dispersal of rhizomes. Fallopia x bohemica is often underreported and is invasive throughout mainland Europe and in some states of America.
Railway-yard knotweed (Fallopia x conollyana)
First discovered in Wales in 1983, this hybrid plant has been reported to be a cross between Fallopia japonica and F. baldschuanica , having been discovered growing in close proximity to both plants in disused railway-yards in both the Czeck Republic and Germany. This hybridization theory was later confirmed by artificial cross-pollination within a lab. The plant has a similar structure and appearance to Fallopia japonica, with the stems having a propensity to bow over after reaching a height of 2m. It can be difficult to tell this hybrid apart from Japanese knotweed itself, as the plant’s leaf shape and growth can often mimic its parent as it appears post-herbicide treatment.
Russian Vine (Fallopia baldschuanica)
Commonly known by gardeners as ‘mile-a-minute’, Russian vine is a fast-growing relative to Japanese knotweed  which also shares some physical traits which often lead to its misidentification. Whilst its flowering structure and masses of green leaves are arguably a red herring, the key difference here is that the vine is a climbing plant that relies on other structures, be it plants or buildings, to grow upwards, as opposed to Japanese knotweed which supports itself.
Hedge Bindweed (Calystegia sepium)
Bindweed is often incorrectly identified as Japanese Knotweed. This is because Bindweed leaves are very similar to Japanese knotweed’s heart-shaped pointed tipped leaves . Bindweed leaves also alternate along the stem, just like Knotweed. Like Japanese Knotweed, Bindweed can cover a large area very quickly and start to appear in spring. A key distinguisher of Bindweed is its large pink and white trumpet flowers which start growing in early summer, these are unmistakably different to knotweed’s small, creamy white flowers.
Japanese knotweed is technically a herbaceous perennial plant. The plant is often mistaken for a shrub due to the large amounts of foliage it produces. Common shrubs such as lilac, poplar and dogwood (above) also feature similarly-shaped leaves, which can lead to misidentifications. This woody shrub is often mistaken for Japanese knotweed because of the similarity in its leaf shape and colour. During spring these bright leaves are accompanied with creamy white flowers which also make it easy to confuse with Fallopia Japonica. The uninitiated may also be drawn to its bright red woody stems that grow throughout winter . Being a shrub, this plant can also grow readily and may appear to be invasive, when in fact it can easily be trimmed back. The key difference between this plant and knotweed is its woody stems which can be stripped down, as opposed to the hollow Japanese knotweed canes that can be snapped.
Heart-leaved houttuynia (Houttuynia cordata)
This herbaceous perennial is rhizomatous, just like Japanese knotweed, and also features heart-shaped leaves which may cause alarm bells to ring. Despite these initial similarities, however, there are some key differentiators which make it easy to distinguish. Heart-leaved houttuynia produces tiny yellow flowers in spikes , as opposed to the large spikes of creamy-white flowers of Japanese knotweed. The plant also grows to a maximum height of 30cm, making it much smaller in stature than even the dwarf variety of Japanese knotweed.
Red Bistort (Persicaria amplexicaulis)
Also known as Himalayan fleece, Red Bistort is native to China, Pakistan and the Himalayas. Another herbaceous perennial, this plant is a close relative of Japanese knotweed and grows to a maximum height of 1.5 metres. The flowers grow in similar spikes, however they are typically white or pink in colour, as opposed to cream . The stems are hollow, just like Japanese knotweed and leaves are arranged alternately along the stems as well. Red bistort’s stems are usually much thinner, typically less than 1cm in diameter.
Himalayan Balsam (Impatiens glandulifera)
This invasive non-native plant grows throughout the year and can reach a height of 2.5 metres, reaching a similar height to Japanese knotweed. The stems are also hollow with leaves arranged in a similar alternate fashion. The leaves are a key differentiator, with Himalayan Balsam’s being much long and thinner than Japanese knotweed’s, with each leaf also featuring a pink mid rib. This plant can often be found growing near Japanese knotweed on watercourses , but spreads via seed dispersal as opposed to rhizome translocation.
Broadleaved Dock (Rumex obtusifolius)
More commonly known as dock leaf, this plant’s most obvious similarity with knotweed is its titular leaf which is broad and green, however the physical similarities they share ends there. Once fully grown, the leaves themselves are much larger than Japanese knotweed and the plant itself is shorter in stature than knotweed, growing up to 1 metre tall. Although leaves are arranged alternately along stems, they will tend to form in tighter knit rosettes closer to the ground , as opposed to the larger bushy formations that Japanese knotweed develops. Stems, whilst being similarly hollow, contain a foamy-pith, and often resemble the Japanese knotweed as it dies back in winter.
Bamboos is one of the fastest-growing plants in the world , so it’s unsurprising that it’s often confused with the similarly speedy Japanese knotweed, especially when you consider the likeness between the way the plants grow. Like Japanese knotweed, bamboo grows in nodes from difficult to eradicate rhizomes. At closer inspection there are some key differences: although shoots look similar, Japanese knotweed will snap when bent, whereas bamboo will not yield easily. The leaves are also very different, growing up to 50cm long, as opposed to Japanese knotweed’s smaller heart-shaped leaves.
Himalayan Honeysuckle (Leycesteria formosa)
This plant is considered an invasive plant in Australia and New Zealand, whilst being native to the Himalayas and China. It has bamboo-like stems that can be easily snapped, which often leads to it being mistaken for Japanese knotweed. Besides the stems, though, there are many differentiators including the formation of leaves opposite to another along the stem (as opposed to alternating) and a lack of purple speckling along the stems. The flowers form in pendulous racemes, as opposed to spikes, and also feature deep purple berries  which makes it much easier to distinguish from Japanese knotweed.
Horsetail (Equisetum arvense)
Horsetail will only be mistaken for Japanese knotweed when it is in its infancy. Its shoots can grow at a fast pace in spring and may also appear in a large quantity. These strobili die back after they’ve released their spores, however, and are soon replaced by green stems that are segmented into nodes, similar to Japanese knotweed. As soon as Horsetail’s signature brush-like growth forms it becomes apparent that this plant is very different to Japanese knotweed, however it’s still an invasive plant that should be dealt with .
Buckwheat (Fagopyrum esculentum)
Despite its name, Buckwheat is not wheat or grass. The plant is closely related to plants, such as knotweed , which explains why it is sometimes confused for it. Buckwheat closely resembles its relative when first shooting. Its stems develop marked nodes and its leaves are also arranged alternately along its stems. The leaves are, however, a much different shape to knotweed, often angular and thin, with the base of the leaf clasped around the stems. The flowers are larger and develop as pink or white clusters at the end of stems.
How can I tell if I have Japanese knotweed?
Japanese knotweed infestations can come in all shapes and sizes, so spotting an infestation is not always easy. In overgrown gardens, a patch of Japanese knotweed could easily be lost, especially during the winter when the plant has died back. There are, however, a handful of neighbourhood risk factors which the RICS have suggested are often linked with Japanese knotweed infestations.
- The property is close proximity to a water source, such as a canal, lake, culvert or pond.
- Nearby public or private footpaths, roads, railways, motorways, or other public land that may have been left to grow.
- Any large open public space, such as a car park, derelict homes, cleared or unused land.
- Properties close to large industrial buildings, workshops and storage depots are also considered to be risk factors.
How do I know if I have Japanese knotweed?
Getting a positive identification of Japanese knotweed can be difficult if you’re unaware of the seasonal changes the plant goes through, or the numerous copycats that it can be mistaken for. Japanese knotweed can cause damage to property and the environment, so it’s important to be vigilant and pay take note of any unfamiliar plants growing on your land.
If you have any plant matter on your land that resembles these descriptions or images then it’s worth taking photos and sending them to us using the form on the right. We could help you recover the costs of treatment, especially if you’ve bought a property with Japanese knotweed or if it has entered your property from a neighbouring property.
Write us a message, chat with us, or give us a call on 0151 668 0561.
 Cornus Profile – RHS
 Docks Profile – RHS
 The Book of Bamboo