Japanese knotweed has hollow, bamboo-like stems with purple or red speckles, grows in a zig-zag pattern from node to node, and has shield or heart-shaped leaves with a flat base and pointed tip. In late summer it carries clusters of small creamy-white flowers, and in winter it dies back to brown, hollow canes. In spring, new shoots are red or purple and look a little like asparagus. If you think you have it, leave it alone, take photos and get a specialist survey.
Key features to look for
Japanese knotweed (Reynoutria japonica, also known as Fallopia japonica) is an invasive non-native plant. In the UK it spreads by underground rhizome and by fragments of stem and rhizome, not by seed. Its appearance changes a lot through the year, but a few features hold good whenever you see it:
- StemsHollow, upright and bamboo-like, with raised nodes along their length. Green with distinctive purple-red speckles, turning brown and woody in winter.
- Zig-zag growthLeaves grow alternately from each node, so the stem bends slightly at every leaf, creating a zig-zag pattern.
- LeavesShield or heart-shaped, with a flat or straight base and a pointed tip. Fresh green, smooth and usually around the size of a hand on mature plants.
- FlowersSmall, creamy-white flowers in loose, upright or drooping clusters from the leaf joints, typically in late summer to early autumn.
- Height and densityGrows fast in spring and summer, often reaching two to three metres, forming dense stands that shade out almost everything underneath.
- Winter canesDead, brown, hollow canes that stay standing over winter, often with a thick layer of leaf litter at the base.
What does Japanese knotweed look like in each season?
Spring (around March to May)
New shoots push up from the crown and rhizome as the soil warms. They are red to purple and look a little like asparagus spears, with rolled-up dark red leaves that unfurl as the shoots grow. Growth is remarkably fast: shoots can rise visibly from one week to the next. This is often when people first notice something odd emerging from bare ground, a gravel path or the gap between a fence and paving.
Summer (around June to August)
By summer the plant is at full height, typically two to three metres, with dense green foliage. The stems are green with purple speckles, and the shield-shaped leaves are arranged in the characteristic zig-zag. A mature stand forms a thicket that is hard to see through. Towards late summer, flower clusters begin to appear at the leaf joints.
Autumn (around September to November)
Creamy-white flowers are usually at their peak in late summer and early autumn, sometimes attracting lots of bees. As temperatures drop, the leaves turn yellow and then brown and begin to fall. This is also when the plant moves energy down into its rhizome, which is why late summer and early autumn are the key window for herbicide treatment.
Winter (around December to February)
Above ground the plant dies back completely. What is left is a stand of brown, hollow, brittle canes, often still upright, with the nodes clearly visible, and a mat of dead leaves around the base. The rhizome underground is alive and dormant, ready to send up new shoots in spring. Winter canes are one of the easiest signs to miss, and also one of the most telling.
Common lookalikes and how to tell them apart
Several common garden plants are regularly mistaken for knotweed. The table below sets out the main differences.
| Plant | How it can look similar | How to tell the difference |
|---|---|---|
| Bindweed | Heart-shaped leaves; climbs through fences and hedges | Thin, twining stems that wrap around supports rather than standing upright; white trumpet-shaped flowers; no hollow canes |
| Russian vine | Related to knotweed with similar small creamy flowers | A climber that scrambles over fences and sheds; thin, woody stems rather than thick hollow canes; arrow-shaped leaves |
| Himalayan honeysuckle | Hollow, segmented stems; grows tall in gardens | Leaves grow in opposite pairs, not alternately; drooping strings of white flowers with purple bracts; dark berries |
| Dogwood | Red stems in winter and spring | Woody, solid stems rather than hollow; oval leaves in opposite pairs with curved veins |
| Bamboo | Tall, segmented canes | Canes stay green or woody all year and do not die back; long, narrow, grass-like leaves; no speckles |
| Himalayan balsam | Tall, reddish stems in damp ground | Juicy, fleshy stems that are not hollow canes; pink slipper-shaped flowers; an annual that disappears in winter |
Related plants can also be confusing. Giant knotweed is larger with bigger, more heart-shaped leaves, and Bohemian knotweed is a hybrid that sits between the two. Both are managed in a similar way; see our page on other invasive plants.
Where is knotweed usually found?
Because knotweed spreads through rhizome and fragments, it tends to turn up where soil or cuttings have been moved, or along corridors where it can creep along unchecked. In and around Liverpool, common places include:
- Railway embankments and cuttings, and gardens that back onto them.
- Canal sides and towpaths, including along the Leeds and Liverpool Canal through Sefton and north Liverpool.
- Riverside land, docks and former industrial or brownfield sites.
- Entries (alleyways), waste ground and the edges of car parks.
- New-build sites where topsoil has been imported or ground disturbed.
- Along fences and boundaries, where it can push through from next door.
We see it in all kinds of settings, from terraced streets in Walton to riverside and former industrial land around Garston and gardens in Huyton.
What to do if you think you have found knotweed
- Leave it alone. Do not cut, strim, pull, dig, mow or spray it. Every fragment of stem or rhizome that is moved can grow into a new plant.
- Take photos. Photograph the whole stand, close-ups of stems, leaves and any flowers, and wider shots showing where it is relative to the house and boundaries. Date them if you can.
- Note where it might have come from. Is it next to a fence, an entry, railway land or a neighbour's garden? That helps with the plan.
- Do not move soil. Avoid digging or moving soil or garden waste from around the plant, and never put it in your green bin.
- Think about any sale or mortgage. If you are buying, selling or remortgaging, tell your solicitor and get specialist advice early.
- Get a survey. A knotweed survey confirms the identification, maps the stand and gives you options in writing.
Why you should not treat it yourself
It is natural to want to deal with it straight away, but DIY attempts are one of the main reasons small infestations become big ones. Cutting and strimming scatter fragments. Digging leaves rhizome behind and spreads soil. Shop-bought weedkillers, especially if applied at the wrong time, can knock the plant into dormancy so it seems to have gone, only to reappear later and take longer to deal with properly. Knotweed waste is controlled waste, so cuttings and soil cannot go in household bins or the tip in the usual way. And without records from a professional programme, a buyer or lender may not accept that it has been dealt with. That is why we never give DIY treatment instructions: it is a specialist job.
A brief word on the law, in general terms only: it is not illegal to have knotweed on your land, but it is an offence to plant it or cause it to grow in the wild, and knotweed waste must be disposed of at a suitably licensed site. Where knotweed affects neighbours, councils can take action in some cases. For any dispute or legal question, please speak to a solicitor.
Knotweed and buying or selling a home
Sellers in England are asked about Japanese knotweed on the TA6 property information form, and mortgage valuers look out for it. If you have identified it, getting a survey and a management plan in place early usually makes the process smoother. Our page on knotweed and mortgages explains how surveyors assess it now and what lenders typically ask for, and our cost guide covers what affects the price of dealing with it.
If you are still unsure what you are looking at, send us photos. Our Japanese knotweed experts in Liverpool can usually tell from good pictures whether it is worth a survey, and our Merseyside knotweed survey and removal service takes it from there.
Not sure if it is knotweed?
Send photos or call 07777 659786. Tell us where the plant is and whether a sale or mortgage is involved, and we will advise on the next step.
Frequently asked questions
What does Japanese knotweed look like in the UK?
In summer it forms dense stands two to three metres tall, with hollow, bamboo-like stems speckled purple-red, shield-shaped leaves arranged in a zig-zag and creamy-white flowers in late summer. In winter it dies back to brown hollow canes. In spring it sends up red, asparagus-like shoots.
How can I tell knotweed from bindweed?
Bindweed has thin, twining stems that wrap around fences and other plants, and white trumpet-shaped flowers. Knotweed stands upright on its own thick, hollow, speckled canes with zig-zag growth and small creamy flower clusters. Bindweed does not leave standing brown canes in winter.
What does Japanese knotweed look like in winter?
Above ground it dies back to brown, hollow, brittle canes, often still standing, with visible nodes along each cane and a layer of dead leaves at the base. The rhizome below ground is alive and dormant. These winter canes are easy to overlook but are a strong sign of knotweed.
Can Japanese knotweed grow through concrete?
Knotweed does not usually break through sound concrete, but it exploits existing cracks, joints and weak points, and can push through paving, tarmac, patios and gaps along walls and fences. Its growth can cause damage to lightweight structures and hard surfaces where weaknesses already exist.
Is it illegal to have Japanese knotweed in my garden?
No, it is not illegal to have it on your land. It is an offence to plant it or cause it to grow in the wild, and its waste must go to a suitably licensed site. Councils can act where it affects neighbours. For legal questions, please speak to a solicitor.
Should I cut down Japanese knotweed?
No. Cutting, strimming and mowing spread fragments that can grow into new plants, and they reduce the leaf area that takes up herbicide during treatment. Leave it alone, take photos and arrange a survey.
Can I send photos for identification?
Yes. Clear photos of the whole stand, the stems, leaves and any flowers, plus a wider shot showing where it is, are very helpful. We can usually tell whether a survey is worthwhile. For a sale, mortgage or dispute, a site survey and written report will normally be needed.