Japanese knotweed flowers appear in late summer, and are small, white and very delicate. You may see bees flocking to them, as they often bloom after most other flowers have died. The flowers grow on long thin spikes around 10cm in length.
Japanese knotweed leaves are up to 15cm in length and fairly flat. Arranged in an alternating pattern, the leaves begin a reddish colour in the spring before turning fully green in summer. They are shovel-shaped, although hybrid versions may appear more heart-shaped.
The stem of Japanese knotweed is a hollow culm, similar in appearance to bamboo externally. In spring, the shoots start out reddish-purple, before growing into green with red flecks and rings. In winter, they die back to being brown brittle canes which can be easily snapped.
In early spring, Japanese knotweed can be identified through often random but very hardy purple, reddish-brown shoots that appear through dead foliage. The sporadic growth can happen anywhere, including through pavement cracks and walls.
The root system of Japanese knotweed is very invasive, and can grow through house foundations, boundaries and more. The roots are thick, and while often found around 1m below the ground, they can be found up to 3m below ground.
In winter, Japanese knotweed loses its white flowers and leaves, leaving brown, hollow canes behind in its place. While these may appear dead, if left, they can last the winter and bloom once again in spring.
Why is it Important to Identify Japanese Knotweed?
- Japanese knotweed growth can lead to legal issues.
- It is highly invasive and can grow up to 20cm a day.
- The plant could cost hundreds to thousands of pounds in damage repairs.
- The plant causes material damage to buildings and pavements.
- Rhizomes can interfere with drainage systems.
- It is illegal to allow the plant to spread to neighbouring properties or the countryside.
How Japanese Knotweed is Identified
RICS Approved Survey
RICS (Royal Institute of Chartered Surveyors) surveys are carried out by one of our accredited surveyors here at Japanese Knotweed Specialists. We most commonly carry these surveys out in the warmer months, especially as people begin to prepare their gardens for summer, or as they winter-ready them.
Our expert identification looks for signs of Japanese knotweed and uses the latest RICS and PCA (Property Care Association) Guidance to provide you with an accurate and actionable report.
Dog Detection Surveys
In winter months, we use sniffer dogs to help identify knotweed in areas of thick overgrowth or large expanses of land.
These highly trained sniffer dogs are taught to identify the smell of Japanese knotweed roots and buds and can cover large expanses of land at rapid speed, quickly identifying knotweed before it takes over.
Identifying Young Japanese Knotweed
Roots that are purple, red, or brown
As they sprout, the leaves and stems of a Japanese knotweed plant appear as a reddish-brown colour.
Appearance that’s similar to bamboo
Young Japanese knotweed has ridges and bumps along the stem that look similar to bamboo.
Clustered dead shoots
Japanese knotweed appears to die out in the winter, but this is only temporary. When it starts to grow again, fresh stems will appear alongside dead shoots.
Small shovel-shaped leaves
The leaves can best be described as shovel-shaped, heart-shaped, or spade-shaped. There’s often a much larger surface area closer to the stem with a point at the end of the leaf
Sprouts from dead foliage or building materials
Japanese knotweed can easily grow through cracks in building materials. This growth often causes more damage to infrastructure if left untreated
Plant growth that’s aggressive
In peak season, Japanese knotweed is known to grow up to 20cm a day. Left untreated, it could cause horrendous damage to your property.
When is it Best to Identify Japanese Knotweed?
The best time of the year to identify Japanese knotweed is in the middle of summer.
During early spring, purple shoots will appear above the ground, just as buds form and bloom outward as “spears”. As these grow – reaching up to 2cm daily – they start to form bamboo-like pillars.
In early summer, however, the stems will have matured and developed a purple pattern. At this stage, they begin to grow in a zig-zag, with leaves beginning to sprout.
As the Japanese knotweed identification process can be challenging, depending on the time of the year and the conditions of the environment, we’ve developed a guide to help you understand the timeline of growth and change that occurs in this plant throughout the seasons.
What is the Law Around Japanese Knotweed?
Is it Illegal to Have Japanese Knotweed on Your Property?
It’s not an illegal act for either you or your neighbour to have Japanese knotweed growing in the garden. However, it is illegal to allow Japanese knotweed to spread from your property into a neighbouring area or the countryside.
If you’re caught spreading the plant into the wild through improper disposal, or you’re deemed negligent for failing to control it on your property, you can be prosecuted. Any soil or contaminated materials must be disposed of correctly and it’s advisable to use specialists to do so. At Japanese Knotweed Specialists, we also offer an insurance-backed guarantee for our customers as peace of mind if they want to sell their home in the future.
Is it a Legal Requirement to Remove Japanese Knotweed From Your Property?
It’s not a legal requirement to remove Japanese knotweed from your property, but it might be easier to treat the issue sooner rather than later. If the plant is growing on your property, you’ll need specialists to safely remove it. Dependent on the site, appropriate forms of professional disposal could be:
- Excavation, transfer, and disposal of contaminated soil off-site
- Excavation and on-site burial
It’s important to allow specialists to completely remove and eradicate the plant as DIY attempts could lead to the weed spreading even further.
What Legislation Covers Japanese Knotweed?
Japanese knotweed can be a nuisance for both domestic and commercial premises, that’s why it’s covered under several laws. These pieces of legislation include topics such as the approach to disposing of contaminated soil and the spread of the plant into the wild.
Japanese knotweed is covered under the following laws:
- The Environmental Protection Act
- Environmental Agency Knotweed Code of Practice
- Invasive Weed ASBO: The Anti-Social Behaviour, Crime and Policing Act 2014
- Wildlife and Countryside Act 1981
- Property Care Association Code of Practice
If you suspect Japanese knotweed is growing in and around your property, request a survey from us today and we’ll investigate it for you.
Identifying Japanese Knotweed in Spring
In early spring, the reddish-purple shoots begin to appear. These soon turn to smaller reddish-green leaves and begin to grow at a rapid pace as we head into early summer.
Growth will be sporadic, and shoots could appear anywhere, not necessarily near dead canes from the previous winter. By the end of spring, the knotweed will be a metre or so high and begin to turn a darker green.
Identifying Japanese Knotweed in Summer
In summer, when this invasive plant is at an average of between 2-3 metres high in full bloom, the spade shaped leaves and spiky stems with creamy white flowers make Japanese knotweed identifiable in peak summer.
With the ability to grow up to 10cm a day in the height of summer, Japanese knotweed will be noticed by the end of August if it hasn’t already been. The combination of sheer height and density of Japanese knotweed in the summer makes this plant easily identifiable.
Japanese knotweed is a good source of nectar and may attract bees and other pollinating insects as full bloom begins around late August. This is another way to identify it compared with other plants
Identifying Japanese Knotweed in Autumn
The appearance of Japanese knotweed in autumn will have very similar traits as in late August, as the flowers will potentially be in full bloom until early October.
Towards the end of October and through to November, the shield shaped leaves will start to wilt and turn yellow, and the stems will become dark brown in colour and start to become dormant, appearing brittle.
Identifying Japanese Knotweed in Winter
By wintertime, around November, leaves will have fallen, and the dark brown canes will appear brittle, and may start to decompose. Whilst in winter Japanese knotweed remains dormant above ground, below ground the rhizomes are still present and will continue to spread. This is when our highly trained sniffer dogs are used to detect stubborn roots and buds underground.
At the end of winter, around February, the new season’s shoots may already begin to appear. These could be growing near clusters of dead stems, other foliage, or from cracks in cement or brick.
Where Does Japanese Knotweed Grow?
Japanese knotweed is rife across the UK, with hundreds of active cases around the country. It has the versatility to grow anywhere, especially in areas where the soil has become contaminated. As it can spread very quickly, it’s also difficult to control if not treated correctly.
Some of the places you might find Japanese knotweed include:
- Near dead foliage or dead stems in your garden
- Around ornamental garden plants or vegetable plots
- Growing through cracks in cement or brick
- On new- build construction sites
- In overgrown gardens that have seen little maintenance
- In well-kept gardens
Fortunately, Japanese knotweed is not strong enough to grow through secure materials, but it can force its way through any broken building materials, including rubble. If it’s left to grow, it can lead to major structural damage. For example, it has the strength to move underground pipework or lift up paving slabs.
Whilst the plant might look pretty to some, it can majorly disrupt other plant life on your premises. Where it is able to rapidly grow, its density can starve other plants, killing them off altogether. This is another reason why you can be prosecuted if it spreads into the countryside. Even well-kept and groomed gardens can fall victim to the invasive weed – all it takes is a small piece of rhizome or contaminated soil to be mixed into your garden
See More Japanese Knotweed Pictures
Don’t rely on guesswork, especially when it comes to such a destructive and costly plant. When attempting to identify Japanese knotweed, it’s helpful to look at pictures – many of which highlight just how invasive this plant can be.
But if you’re still unsure – always contact a specialist for a professional survey. Misidentifying Japanese knotweed can lead to costly and damaging consequences.
Plants That Can Be Mistaken For Japanese Knotweed
On your journey to identify Japanese knotweed, you could easily mistake another plant that isn’t invasive for knotweed. Here are three common plants that people often mistake for Japanese knotweed.
Russian Vine (Fallopia baldschuanica)
- As fast-growing as Japanese knotweed.
- Same colour leaves and flowers.
- Unlike Japanese knotweed, Russian Vine is very disorderly in appearance.
Himalayan Knotweed (Persicaria wallichii)
- Similar stem to knotweed, so they may look alike when not in bloom.
- Spreads densely like knotweed.
- Their main difference is that their leaves are half the size and their flowers are pink.
Houttuynia (Houttuynia cordata)
- Houttuynia is a perennial plant also with heart-shaped leaves and white flowers.
- Grows at a similar time and rate to Japanese knotweed.
- However, it is much shorter with a large yellow stigma when compared to Japanese knotweed.
- As it sprouts from the ground, peonies have the same reddish-brown colour as Japanese knotweed.
- Their shoots are spear-like at first, similar to Japanese knotweed before the leaves grow through.
Dogwood (Cornus sanguinea)
- Similar to Japanese knotweed, Dogwood showcases a brilliant red colour on its stem.
- Its stems are also thin, just like Japanese knotweed.
- They were also introduced as an ornamental plant and have a similar leaf structure to Japanese knotweed.
Bindweed (Convolvulus arvenis)
- Bindweed has the same shovel-shaped leaf appearance as Japanese knotweed
- Both plants have white flowers, but their designs vary
- Bindweed tends to climb around structures or up walls, whereas Japanese knotweed can stand independently.
It is highly important to make sure you have an expert to carry out Japanese knotweed identification to determine whether you have an infestation or not. Failure to do so can lead to the plant quickly spreading across your premises and neighbouring properties, leading to damage.
Experts like our team here at Japanese Knotweed Specialists will be able to conduct a full survey, provide visual identification, or in winter, use a dog detection survey to sniff out knotweed underground.
Get in touch with the experts at Japanese Knotweed Specialists today to find out how we can create a treatment and removal plan.
Japanese Knotweed Specialists are the leading invasive species identification and removal professionals in the UK, capable of treating and disposing of various aggressive plants.
If you suspect growth of Japanese knotweed on your property, you have a legal obligation to prevent it spreading. Contact a specialist today to ensure peace of mind – we’ll help you identify and treat any infestations.