Japanese knotweed (Fallopia japonica var. japonica) was introduced into Europe in the mid-19th century by Philipp Franz Balthasar von Siebold, a German botanist and physician living in The Netherlands. In 1850, von Siebold sent a specimen of Japanese knotweed to Kew Gardens in London and by 1854, knotweed had travelled as far as the Royal Botanical Gardens in Edinburgh. Just over 30 years later, in 1886, Japanese knotweed was found growing in the “wild” for the first time, in Maesteg, south Wales.
Now, the plant is found in over 70% of UK hectads – 10km × 10km grid squares used to measure animal and plant distributions – although it is worth noting that this does not necessarily indicate high abundance in all areas. It is also established across mainland Europe, North America and the southern hemisphere. This global spread is astonishing – particularly as, to date, it has only occurred via plant fragments (vegetative) and not from (viable) seed.
In the UK alone, it is estimated that controlling Japanese knotweed costs the economy around £170m every year. There are at least 15 different active control methods and herbicides used in the country, and an extensive control industry has built up around the plant.
But, until now, there has never been a study of the scale needed to truly test how effective these treatments are. They are being sold to home and land owners with no unbiased research to back up their worth. However, we have recently completed the largest Japanese knotweed field trial ever conducted globally, and working with academic and industry partners, found the best way of treating the plant long term.
- Control not kill
- Ask the Gardener: Untangling the mystery of how to kill knotweed
- How do you get rid of Japanese knotweed?
- Japanese Knotweed—Polygonum cuspidatum (Fallopia japonica)
- Plants commonly mistaken for Japanese knotweed
- Japanese knotweed Removal
- Plants Mistaken for Japanese Knotweed | Pictures
- Plants Mistaken for Japanese Knotweed
- Japanese Knotweed Identification
- Useful Links
- FREE Japanese Knotweed Identification
- What does Japanese knotweed look like?
- Japanese knotweed in spring
- Japanese knotweed in summer
- Japanese knotweed in autumn
- Japanese knotweed in winter
- Japanese knotweed leaves
- Japanese knotweed flowers
- Japanese knotweed rhizome
- Japanese knotweed stems
- Japanese Knotweed Identification Video
- Do you think you can identify Japanese knotweed?
- Other Types of Knotweed
- Plants Mistaken for Japanese Knotweed
- Everything you wanted to know about Japanese Knotweed but were too afraid to ask
- Related posts:
Control not kill
The key to our approach was to understand the plant, in order to control it. Japanese knotweed’s ease of spread and rapid growth from a deep rhizome (root) system was initially prized for planting schemes. However, from an ecological perspective, these plant traits are precisely why it has become a huge problem for native biodiversity and, increasingly, wider society.
Rapid growth from early in the growing season (February onwards in the UK) excludes most native plants from well-established Japanese knotweed patches (known as “stands”). This is because the dense canopy of leaves shades out other species. This shading effect is amplified as insects do not graze on knotweed plants, and native diseases don’t keep the plant in check either. Knotweed also produces a thick leaf litter, and chemicals that inhibit the germination and growth of native plants. It dominates non-native habitats, displacing native plants and altering how local ecosystems function – for example, in soil nutrient cycling.
During our research, it became apparent that because a Japanese knotweed stand contains significant underground and spreading biomass, we would need to do large field trials, to reflect real world conditions. So, we set up 58 different 15 metre × 15 metre (225 square metre) field trial plots, located in south Wales (UK), and repeated each method three times in these areas.
Between 2011 and 2016, we tested all control methods and herbicides used for controlling knotweed in the UK, Europe and North America – 19 in all. This experiment continues to be unique in terms of scale, duration and scientific rigour. But it is plain to see why this research has not been conducted before – the commercial cost has been (conservatively) estimated at £1.2m. However, given the ongoing costs of managing knotweed in the UK, the value of the experiment is self-evident.
Our research has highlighted the most appropriate way to treat established Japanese knotweed stands and, surprisingly, a number of other methods which are poor or totally ineffective at field scale. We now know that glyphosate-based herbicides are significantly better than all other herbicide groups currently used for knotweed control, and that physical methods such as covering up and cutting down knotweed simply do not work. Importantly, we are not describing eradication (which is almost impossible to acheive), but rather a type of extended “dormancy” where the plant does not grow above ground.
Plot comparison, before and after treatment. © Advanced Invasives 2018, Author provided
Additionally, we have also found that understanding when to apply the herbicide by considering the biology of the plant, specifically the seasonal surface-rhizome resource flows, is critically important. From this, we have defined a new patent pending approach to Japanese knotweed treatment, The 4-Stage Model™, which links herbicide selection and application with the seasonal surface-rhizome flows in the knotweed plant.
We are now working to replace outdated guidance based on short-term experiments and anecdotal information. We’re discovering how best to tackle invasive plants in real world conditions, informed by the evidence of what actually works.
While we acknowledge the current political debate surrounding glyphosate use and licence renewal for this herbicide, the effective outcomes of using glyphosate-based treatment seasonally requires lower doses of herbicide across the whole treatment life cycle. It is also more sustainable than other control methods that do not work.
All in all, our ongoing experimental approach delivers a more affordable knotweed treatment that is also more environmentally friendly than traditional, blanket application of herbicides.
Ask the Gardener: Untangling the mystery of how to kill knotweed
What to do this week: Wrap the lower trunks of young fruit trees to protect them from hungry rodents that gnaw bark. Spray prized evergreens with a repellent where deer are a problem. Fill bird feeders with black oil sunflower seeds to attract cardinals. Hang suet bricks for woodpeckers. Top off Christmas tree stands with water frequently. Move houseplants into south- and west-facing windows if they need more light. A humidifier benefits both houseplants and people in winter.
Q. I have tried weed killers and pulling at a 30-foot stand of 6-foot tall Japanese knotweed to no avail. Every year it grows farther into our lawn. Do you know how to get rid of it?
A. Japanese knotweed is the Godzilla of the plant world. If people realized how almost unkillable it is, they wouldn’t be so casual about spreading it around through infected fill and careless mowing. Perhaps the single best tip I can give my readers is not to buy or move soil from another site for fear of introducing this towering plant (or another invasive) into their yard. The good news it that the frothy-white late summer seeds seem to be sterile, but a piece of stem or root can start a new colony of bamboo-like stalks. It took me more than 20 years of decapitating and poisoning to defeat just two measly stalks. In England, professional knotweed removal is an industry because it’s hard to sell or get a mortgage for an infected property. But in the United States, you’re pretty much on your own.
So what can you do? Many have concluded that the only way to kill knotweed is to apply glyphosate (Roundup, Rodeo) between August and the first hard frost — year after year after year — until it stops resprouting. Most attempts fail because people don’t know that timing and persistence are essential. The tops are relatively easy to kill, and at first it looks like you’ve had total success with a single spraying. But the roots are your target, and you can reach them only when the sap is retreating downward in the fall. Glyphosate is widely considered the most effective herbicide for knotweed, but it will kill any other greenery it contacts. Be careful not to get spray on yourself or desirable plants. Some people inject it directly into the knotweed stalks. If your abutter has knotweed, too, you need to work together for total control, as it can travel 20 feet underground before popping up.
Many people abhor using glyphosate or other herbicides. Others make an exception for Japanese knotweed, having concluded it is very difficult to control and perhaps impossible to eliminate by organic methods. One alternative is to cut down the stalks as soon as they appear, and to keep cutting them down before they can photosynthesize. Treat each living stalk like toxic waste to be incinerated. Bag stalks rather than composting them, and, when in doubt, call your local Department of Public Works for disposal instructions. The New England Wild Flower Society recommends leaving black plastic bags of cut stalks in a sunny place for several months to fry them before disposing of them. Do not try to pull on, dig up, or weed the deep, massive roots. You can’t succeed, and you may stimulate more spreading. Do not disturb or move soil that’s within 20 feet of knotweed; that may encourage spreading, too. Think of this as a sleeping dragon you don’t want to awaken.
Clear the top growth of Japanese knotweed (Fallopia Japonica) away during the winter, after it has been killed by cold. Then carefully cut down and bag any new growth as soon as you see it. Think of knotweed control as your new hobby.
Q. I read somewhere that peanut shells make a good fertilizer for vegetable gardens. If so, how should one apply them? Mix them into the soil? I have been saving bags of shells of unsalted, roasted peanuts.
A. Pioneering black scientist George Washington Carver discovered more than a century ago that growing peanuts can help replenish exhausted soils. Rather than mixing the shells directly into your soil, however, add them to your compost pile. They take about three years to break down — less if you grind or break them up first. So crush those bags of shells. You can also use them as a nutrient-rich, weed-free mulch, perhaps combined with cottonseed meal first to help keep them from compacting when it rains.
Note to Readers This is my last garden column until March, so hold your questions until then, please. See you in 2019.
Send questions and comments, along with your name/initials and community to [email protected] Subscribe to our newsletter at pages.email.bostonglobe.com/AddressSignUp. Follow us on Facebook and Twitter @globehomes.
How do you get rid of Japanese knotweed?
Farmers burning Japanese knotweed plant waste have further legal obligations to follow.
Many people oppose using chemicals to treat weeds and plants in the garden. However, with a plant as tenacious as Japanese knotweed, it is the safest, most-recommended option.
When using weed-killers or root-killers, make sure you only use approved chemicals. Always follow the manufacturer’s instructions.
The Royal Horticultural Society recommends using a glyphosate-based weed-killer to tackle Japanese knotweed, particularly Scotts Roundup Tree Stump and Root Killer.
You should cut back the plant stems before applying.
It can take three years to fully treat Japanese knotweed, so plants will have to be resprayed every year. Try to avoid any other plants when you spray.
Get the professionals in
There are many companies offering their services to dispose of Japanese knotweed. Check out the British Association of Landscape Industries website, as recommended by the Royal Horticultural Society, for a list of its members who treat invasive species.
Photo credits: FLPA / Paul Miguel/REX/, FLPA/REX/
Smartweed (Polygonaceae) family
Fallopia japonica, Pleuropterus zuccarinii, Polygonum japonicum, P. zuccarinii, P. sieboldii de Vriese, Reynoutria japonica, Japanese bamboo, Mexican bamboo, Japanese polygonum, Japanese fleeceflower, false bamboo, Kontiki bamboo, bombascus.
Origin and Distribution:
Japanese knotweed was introduced from eastern Asia in the late 1800s as an ornamental, but soon escaped from gardens to colonize disturbed areas. By the 1960s it had spread to local infestations from Maine south to Virginia and west to Indiana. Today it is found from Nova Scotia to the Carolinas and west to Minnesota and Iowa, as well as in Colorado, Utah, and coastal areas from Washington to Northern California. It is found throughout much of Ohio, especially in urban and suburban landscapes, roadsides, gullies, and waste areas. It is particularly troublesome along riverbanks, edges of ponds, and other wet areas. It is often associated with moist but well-drained sites with nutrient-rich soil, and it tolerates semi-shaded environments. It has also been planted in sandy sea-shore areas where it stabilizes soil and withstands salt and low nutrients.
Japanese knotweed is an erect, broad-leaved, semi-woody perennial that spreads by long rhizomes and occasionally by seeds. The plant forms dense clumps that exclude other plants, and radiates rapidly to form patches that can be as large as 1 to 3 acres. It is one of the most persistent, and hardy of weeds, and it tolerates many control measures. Japanese knotweed is an invasive plant that can overrun natural areas, gardens, yards, roadsides, and utility and railroad rights-of-way.
The root system is fibrous, but rhizomes are white when young, becoming brown, thick, and woody with age. Rhizomes have prominent nodes with dark papery sheaths. They may be shallow or deep, and are responsible for the spread and persistence of this weed.
Seedlings and Shoots:
Young shoots are reddish, with mostly heart-shaped leaves. Because seed production is uncommon, true seedlings are uncommon. Most young shoots arise from rhizomes.
Stems are erect, tall (up to 10 or more feet for mature stands), and hollow except at the prominent, swollen, knot-like nodes. The stems are thought to resemble those of bamboo. Attached to each node and surrounding the stem is a light green to brown, hairless, papery sheath. Stems are round and smooth, red-brown at the base, and mottled green toward the tip. Stems die back to the ground during winter, but semi-woody stem bases persist.
Leaves are alternate (one per node), broad, flat to round at the base, tapering to a pointed tip, and attached by long petioles. The upper leaf surface is dark green and the lower surface is pale green.
Small, greenish white flowers are clustered along branching panicles arising from upper leaf axils. Plants are unisexual, with male and female flowers on separate plants. Male flower stalks are mostly erect and female flower stalks are drooping. When blooming (July to September), the plant puts on an attractive floral display befitting the common name ‘fleece flower’.
Fruits and Seeds:
Rarely produced fruits have three triangular papery wings surrounding a single dry, brown, triangular seed. Fruits are rare because colonies seldom contain a mixture of male and female plants.
Japanese knotweed resembles bamboo because of the robust hollow stems with distinct nodes and internodes; however, true bamboo is a grass. The broad and pointed Japanese knotweed leaves can be mistaken for Broadleaf dock (Rumex obtusifolia), but docks lack rhizomes and the tall, spreading habit of Japanese knotweed. Other less invasive relatives (such as P. virginianum) grow from similar rhizomes and are difficult to eradicate.
Japanese knotweed shoots resume growth in early spring, reaching a fast pace (reportedly 2 to 4 inches in a single day) and attaining heights over 10 ft by late summer. Plants form dense colonies, spreading by rhizomes that can extend up to 65 feet. New colonies can regenerate from as little as a 1-inch piece of rhizome, which can easily be transported wherever soil is moved. Rhizomes send out shoots from April to August, even from a depth of over 3 feet. Shoots can even be initiated from internode tissue. Japanese knotweed exhibits great tolerance to most herbicides. It is reported to be a poor invader into grass cover and can be crowded out by taller trees. It does not survive frequent mowing.
Japanese knotweed has been used as a folk medicine in eastern Asia; however, this species contains tannins that were found to be carcinogenic. Large quantities of tannins were found to inhibit digestive enzymes in rats. Some chemicals isolated from Japanese knotweed have antimicrobial properties, others have been used as antioxidants and antimutagens in cancer research. Other chemicals isolated from this plant have been used to promote healing of burns, and still others to enhance the immune system and cardiac functions.
Facts and Folklore:
Dense stands of Japanese knotweed exclude native and other desirable vegetation and reduce wildlife habit. It decreases water flow through rivers and streams and thereby contributes to flooding. It is a long-term threat because it occupies edges of woods and waterways that are valued for biological and visual diversity. It is one of the most troublesome weeds along railway rights-of-way, and is said to create a fire hazard in the dormant season.
Japanese knotweed is highly regarded for its attractive flowers and has been planted by beekeepers for its nectar. It is also prized for its tolerance of harsh conditions like rocky soils with limited nitrogen and low pH. It has been planted along highways to control soil erosion and has been used for revegetation of strip-mine spoil and to stabilize land affected by volcanoes.
Japanese knotweed has caused damage to sidewalks and parking lots where shoots have been able to grow up through concrete.
Fast-growing branch tips picked in spring are said to be have a unique almond-like flavor when prepared in the manner of rhubarb pie.
Japanese knotweed was used in folk medicine as a laxative, but contains tannins that are carcinogenic and inhibitors of digestive enzymes.
The dense, hedge-like growth of Japanese knotweed was commonly used as a screen around out-houses.
Japanese Knotweed—Polygonum cuspidatum (Fallopia japonica)
Japanese knotweed is an invasive that grows quickly and aggressively, forming dense thickets. It thrives especially in riverbanks, roadsides and moist areas.
Click on images to view full-size
Identification and Control Information (each will open in a new window)
- Maine Invasive Plants: Japanese Knotweed — Maine Natural Areas Program
- Fact Sheet with Description and Control Methods —Invasive Plant Species Assessment Working Group
- Fact Sheet: Japanese Knotweed —United States Department of Agriculture
- Fact Sheet with Description and Control Methods —Penn State College of Agricultural Science Cooperative Extension
- Species Identification Card: Japanese Knotweed —Gulf of Maine Research Institute, Vital Signs Program
- Fact Sheet with Identification Tips and Control Methods —King County, Washington Department of Natural Resources and Parks
- Fact Sheet with Description and Management Options —Plant Conservation Alliance’s Alien Plant Working Group
- Stop the Spread of Invasive Knotweed brochure —King County, Washington Department of Natural Resources and Parks
More Information (each will open in a new window)
- Invasive Alien Plant Species of Virginia: What are Invasive Alien Plant Species and why are they a problem?—Virginia Department of Conservation & Recreation
- Alien Plant Invaders of Natural Areas brochure —Plant Conservation Alliance
- What the heck is an invasive plant brochure —Plant Conservation Alliance
- Read Your “Weeds”–A Simple Guide to Creating a Healthy Lawn —National Coalition for Pesticide-Free Lawns
It is the policy of the State of Maine to minimize reliance on pesticides. The Maine Department of Agriculture and the Maine IPM Council encourage everyone to practice integrated pest management and to use pesticides only as a last resort. The mention of pesticides in the fact sheets linked to these pages does not imply an endorsement of any product. Be sure that any product used is currently registered and follow all label directions.
Plants commonly mistaken for Japanese knotweed
Japanese knotweed can halt mortgage applications, so it’s important it’s identified correctly.
A lot of the calls we receive are from anxious homeowners and potential buyers, who have spotted a suspicious looking plant that has grown rapidly, wasn’t there last year and they’ve been told by a friend that it may be knotweed.
Our advice in this situation is not to panic. Take photos of the plant and the area it’s in. We offer a free Japanese knotweed identification service from a photo. This is a great first step if you’re not completely sure what the weed is and are not ready to commission a full survey. We do not charge for this identification but we do have a JustGiving page to support our chosen charities.
On average, around half of the images we receive each week are not knotweed. There are many plants that look like Japanese knotweed and have similar characteristics. The plants we find that are most commonly mistaken for Japanese knotweed are:
- Bindweed (as pictured above)
- Russian vine
- Broadleaf dock
- Ground elder
While these plants do not contain all the features of knotweed, they have enough of a similarity to cause anxiety. The leaf shape in bindweed is heart shaped and is comparable to knotweed; however bindweed does not have the flat edge like knotweed does. Russian vine has similar white flowers and has the ability to grow rapidly, quickly overwhelming other garden plants. Knotweed canes in the winter have a very similar appearance to bamboo, which is often why it is not spotted during this time.
Take a look at our Japanese knotweed picture gallery and our identification videos to aid you in identifying knotweed throughout the season.
Japanese knotweed has some very distinctive features, once you know what to look for:
- Spade shaped leaf
- Red speckled stem
- Zig zag formation
- Creamy-white flowers in summer
Be aware of bonsai regrowth, which often occurs after glyphosate based herbicides are applied. Bonsai growth looks very different to normal Japanese knotweed, with much smaller leaves and spindly stems.
If you find a plant and think it’s Japanese knotweed but are not completely sure, email your pictures to [email protected] and we will be able to assist you. Or alternatively call 01932 868 700 and one of our consultants will be happy to help.
Japanese knotweed Removal
8. Make sure the work is guaranteed with an insurance backed guarantee (IBG) Guarantees typically range from 5 to 10 years and you need to be assured that these are worth the paper they are written on (see 3 above). Read the small print and know where the liabilities lie. Be aware that a lot of knotweed companies will downplay this element or offer alternatives without the same level of financial security. Also consider the security of the insurer where an IBG is provided. We are one of very few companies in the UK providing an IBG backed by an “A” rated insurer at Lloyd’s.
9. “Consider the lilies!” If you are concerned about the environmental impact of the removal method, killing other plants etc – question the environmental credentials of the contractor. Understanding the wider impacts of dealing with this invasive species is all part of the job for a true expert.
10. Choose to work with someone you like and trust After all, it’s your property they’ll be working on and you want them to leave the site clean and tidy afterwards. You need to be reassured that they’ll continue to monitor the site after the initial treatment and will deal swiftly with any regrowth should it occur. If you don’t choose the right contractor, you could end up disappointed in the work, feeling swindled and needing someone else to finish the job properly when the knotweed pokes its new shoots up again next year.
The best option for homeowners wishing to try the DIY route is to implement a multi-year chemical treatment program. The most popular chemical for Japanese Knotweed treatment is Glyphosate, and it’s readily available in weak solutions from most DIY stores. Stronger variants up to 360 grams per litre are available online.
The young sprouts of Japanese Knotweed
Because Glyphosate is a harmful chemical, we suggest you follow these step-by-step instructions:
Step 1 – Conduct a risk assessment and create an action plan.
Risk assessments are not just for businesses. We advise you to survey the surrounding area and note the following: Children’s playgrounds, communal areas or schools that could be affected by spray drift. Rivers, ponds, stream or other waterways that could be affected. Contact neighbours and ask about pets or children that might be using the garden on the treatment day. An action plan should then be drawn up.
If there’s a risk of spray drifting onto nearby lands such as communal areas or schools, you can contact the landowner or school and ask them to fence off the affected area, or you can delay the treatment until the school holidays when nobody will be using the facilities.
Waterways can be adversely affected by chemicals. If you live close to one, you should first contact the Environment Agency and ask for advice. In most cases, you’ll need to wipe the chemical onto the leaves rather than spraying it. You can also inject the chemical directly into the stem to avoid spray drift.
You should consult your neighbours as part of the risk assessment, and any pets and children kept out of neighbouring gardens for the duration of the treatment. Extra precautions should also be taken with fish ponds.
The best time of year to treat Japanese Knotweed is from late spring through to mid-autumn when the plant is in full growth. If you are relying on the leaves to draw in the chemical and transfer it to the roots, you should ensure that the plant is in full bloom, don’t try to treat the Knotweed in winter or early spring.
Step 2 – Purchase safety equipment.
The type and amount of safety equipment you’ll need will be based on your risk assessment but will most likely include:
overalls, gloves, face mask to P3 standards, face shield, rubble sacks, tarpaulins and sheets.
Step 3 – Check the weather.
Glyphosate is a general non-selective herbicide; this means it doesn’t target a particular species but will affect all plant life. You should ensure the work is carried out on a dry day with no rain forecast for the next 24 hours. We also suggest you avoid windy days if you intend to use a spray applicator.
Step 4 – Treatment.
The best way to treat large areas of Japanese Knotweed is via a garden sprayer, however, for growth near waterways or other sensitive areas, a cloth, roller, brush or sponge can be used to apply the Glyphosate to both the leaves and the outside of the stems (with gloves). Covers and tarpaulins should be used to protect ponds, grass and plants.
We also suggest you inject the chemical directly into the stems of the Japanese Knotweed; the best place is just above ground level near the first node. Professionals use specially designed injectors, but you can cut the stem and pour the chemical directly into it.
Step 5 – Clean up.
Disposable gloves and overalls should be wrapped in a bag and disposed of via normal means. Any Japanese Knotweed that has been cut down to gain access or to inject the stems should be placed in sturdy plastic rubble sacks and disposed of via an approved landfill site. Some local councils offer a free collection service for bagged Japanese Knotweed; others don’t. We suggest you contact your local council for guidance. Current regulations state that only registered waste carriers can transport controlled waste such as Japanese Knotweed.
Step 6 – Repeat treatments.
Professionals usually apply 2-3 treatments per year over a period of between 3-5 years. The exact number depends on the size of the infestation; we suggest you follow this timescale but also keep a close eye on the area and adjust the frequency of treatments accordingly. The cost of a DIY Japanese Knotweed treatment is considerably less than a professional treatment.
For a typical garden with an average-sized Knotweed infestation, you’ll pay around £50 per year for disposable safety equipment and around £100 per year for the chemical. Sprayers cost around £20, and the disposal of any bagged Knotweed could be free if your local council offers a collection service. If not, you’ll need to pay a fee.
Three things you shouldn’t do.
1 – Cutting or strimming is not a realistic option as the roots underground will continue to grow. You’ll also be left with organic material that will need to be disposed of carefully.
2 – Half-hearted attempts to dig out the roots usually fail and sometimes make the problem worse. As previously stated, the roots can be up to three metres below ground level, and all it takes is 0.6grams of root to start a new plant. Unprofessional and incomplete dig outs often create separate strands underground. Japanese Knotweed doesn’t spread by seed but by small amounts of the root being transported to a new location.
3 – Tarpaulins, covers, patio slabs, tarmac or concrete won’t be enough to prevent the growth of this plant. Any attempt to kill off Japanese Knotweed by starving it of sunlight will fail. This invasive species can lay dormant for several years, and the roots can grow underground laterally for up to seven metres, possibly even more if the ground and weather conditions are ideal.
This feature originally appeared HERE.
Plants Mistaken for Japanese Knotweed | Pictures
Plants Mistaken for Japanese Knotweed
I have been compared to many other people in the past, Harrison Ford, David Duchovny, Bono, Robin Williams, and, my personal favourite, Daniel Craig. I must just have one of those faces I guess. Unfortunately, I’m not as good looking, talented, funny, or wealthy as any of the afore-mentioned celebs. Now this leads me on to consider a famous (or infamous) celebrity of the plant family, Japanese knotweed. This poor plant which, in its native land does no more harm than a wood-bug, over here in the UK (and the rest of Europe and the USA) has been transformed (some would say hyped) into a monster of the natural world.
There aren’t many people out there who will profess to like this perennial plant, and few people would blame you for wanting it gone, especially if you are a home owner looking to sell. But it is important to be accurate with Japanese knotweed identification, if only to avoid attacking some other innocent shrub with herbicide. We’ve discussed previously the easy-to-spot visual clues to identifying Japanese knotweed, so in this article we’ll consider a few of the plants mistaken for Japanese knotweed (and a few examples that look nothing like knotweed but still, somehow, get confused for it).
Also known as Pheasant Berry and Himalayan honeysuckle, this beautiful plant has the habit of seeding itself all over the place. However, it can’t really be described as invasive and isn’t a ‘Scheduled’ plant. The image on the left below shows how, at first glance, it could be confused with Japanese knotweed. Looking at the close up photo, however, brings out the differences, the most obvious being the leaves growing in pairs along the stem (Japanese knotweed leaves grow alternately). Nothing to be scared of, just look out for seedlings each year.
Broad leafed dock
Looking at the photo above tells you all you need to know about this commonly misidentified weed; it looks nothing like knotweed! What you can’t see here though is the newly unfurling leaves, which do so in a manner very similar to Japanese knotweed. Dock grows as a multi-leaved plant from individual tap roots and will commonly reach a metre in height with its central flower spikes. Japanese knotweed will normally reach at least two metres in height, with many leaves growing from each main stem and side shoots.
This garden favourite is often a plant mistaken for Japanese knotweed, with its spade shaped leaves and lush green foliage. Although it will send up lots of annoying little suckers if chopped back, that is the extent of its invasive capabilities. Woody stems give this one away (this one is a really quick and easy identifier) as opposed to the hollow stems of Japanese knotweed. So don’t go spraying your lilac bush – spring will bring thousands of beautiful, fragrant white or lilac (of course!) flowers.
Bindweed has to be one the most annoying weeds ever. Give it half a chance and it will climb through all your favourite shrubs and become entangled with every branch, stem and leaf, reaching up to the light by literally wrapping its thin stems around anything that’s available. It’s this characteristic that makes it such a pain to remove – ripping the bindweed stems out often damages any soft stems and leaves on the host plant as well. If you have a lot of patience, you can unwrap each entangled stem all the way down to ground level, where you can then locate and pull out the roots. Again, it’s the leaf shape that makes bindweed look a bit like Japanese knotweed. Look carefully at the leaves and you’ll see that they are heart shaped, with lobes either side of the stalk, which Japanese knotweed does not possess.
It would be difficult to mistake Bamboo for Japanese Knotweed. Japanese knotweed shoots look a bit like bamboo stems but there the visual similarity ends. Japanese knotweed leaves and bamboo leaves are not the same shape at all and knotweed loses its leaves in late autumn, unlike bamboo which usually retains its leaves all year round in the UK. Many bamboos (the ‘running’ variety) will migrate outwards and, because Japanese knotweed also spreads this may be a factor in the two plants being confused.
The name ‘Mile-a-Minute’ might give you some idea of how quickly this vine-like perennial grows, quickly swamping most other plants in the area. It’s closely related to Japanese knotweed – these two darlings can actually create hybrids – but doesn’t have the same fearsome reputation. The leaf shape and flowers are very similar, although the leaves are more arrow-shaped than Japanese knotweed leaves. The lack of tall stems and its scrambling, untidy habit are dead giveaways.
Houttuynia are perennial plants with orange-scented, heart-shaped leaves and small white flowers. The illustration here gives a hint to why houttynia can be mistaken for Japanese knotweed. Although it can easily spread through its rhizomes (it loves moist soils) it generally only reaches 30 centimetres in height. Compare that to Japanese knotweed which grows to three metres tall in the right conditions and it’s clear that the comparison ends there.
This is just a sample of the plants we’ve been asked to identify by customers worried about the possibility of Japanese knotweed on their property. PBA Solutions can help you with our free ‘ID My Weed!’ invasive weed identification service and help discern plants mistaken for Japanese knotweed. Click the link and send us some photographs (close-ups are preferable) of the suspect plant, including any additional details and your name and telephone number. We will do our best to identify the weed for you.
PBA Solutions undertake site surveys to determine if Japanese knotweed is present and document and report on the findings. You can book a Japanese knotweed survey here. Our reports integrate with the mortgage process and site developments, detailing the most appropriate Japanese knotweed solutions.
For further help and information concerning plants mistaken for Japanese knotweed, call our friendly team on 0203 174 2187 or 01202 816134.
Japanese Knotweed Identification
Japanese knotweed, Reynoutria japonica (synomyns: Fallopia japonica and Polygonum cuspidatum) is the most widespread form of knotweed in the UK. Stems form a zig-zag growth pattern, with one stem shoot per node. The leaves are fairly smooth, mid-green in colour, with a characteristic straight top edge, giving the leaf a shield or shovel-type shape.
Knotweed flowers are small creamy-white and form in loose clusters (panicles) in late summer or early autumn. All Japanese knotweed plants growing in the UK are female and therefore do not produce viable seeds. Download our Japanese knotweed identification guide, here (2.3Mb).
- FREE Japanese Knotweed Survey
- Knotweed Management Plan (KMP)
- Damage Caused by Japanese Knotweed
- Japanese Knotweed and the Law
FREE Japanese Knotweed Identification
What does Japanese knotweed look like?
1. Japanese Knotweed Stems: Zig-zag growth pattern, green with red spotting lower down 3. Japanese Knotweed Leaves: Lush green heart or shovel-shaped
leaves with a pointed tip 2. Japanese Knotweed Flowers: Creamy white coloured panicles of flowers (late summer)
|Height||Stem type growth up to 3m tall|
|Japanese Knotweed Leaves||Lush green, heart or shovel shaped leaves up to 200mm long|
|Japanese Knotweed Flowers||Clusters (Panicles) of small creamy white flowers|
|Seeds||Small winged heart shaped seeds (sterile, as no male plant present in the UK)|
Japanese knotweed in spring
The fastest Japanese knotweed growth is during the spring. New shoots that emerge are red/purple and can look like asparagus spears. The leaves are normally rolled up and dark green or red in colour. In late spring, canes can reach up to 3 metres (10 feet) high. The pictures below show Japanese knotweed in spring.
Japanese knotweed in summer
During the summer the knotweed leaves are green and heart/shovel shaped and can be 20cm across. In late summer early autumn small clusters of white flowers will appear. The stems are mostly hollow and bamboo like and the general growth habit has a distinctive zigzag appearance. The photos below show what Japanese knotweed typically looks like in summer.
Japanese knotweed in autumn
In Autumn the dense covering of leaves will remain, however, they start to turn yellow and wilt as we move into September and October. The knotweed plants are still about 2-3 metres tall and the hollow stems start to turn brown. See our images below to identify Japanese knotweed in Autumn.
Japanese knotweed in winter
During late autumn and the beginning of winter the knotweed canes die off and the weed becomes dormant. The leaves turn yellow, then brown and fall off. The canes are hollow, dark brown and brittle and they collapse upon one another. If the area hasn’t been treated, often previous year’s decomposition can be seen underneath. See the images below to identify Japanese knotweed in winter.
Japanese knotweed leaves
Japanese knotweed leaves are shovel shaped (some people think they look heart shaped) with a point at the tip and staggered on the stem (one stem per node), creating a zig-zag stem growth pattern. They’re a luscious green colour and grow up to 200mm long. See the images below for easy identification of the Japanese knotweed leaf.
Japanese knotweed flowers
Elongated clusters of creamy white flowers may appear towards the end of August and early September. The clusters grow to approximately 0.5cm wide and up to 10cm long. The leaves will still be apparent and along with the flowers, it will create a dense foliage. See our images below to identify knotweed flowers.
Japanese knotweed rhizome
Japanese knotweed rhizomes are the underground part of the weed and are actually considered to be underground stems. If it’s fresh, it will snap easily like snapping a carrot. The outside is dark brown and the inside is orange/yellow in colour. The Japanese knotweed rhizome system can grow to depths of 2 metres and can extend up to 7 metres horizontally from the plant. It’s the knotweed rhizome that spread the plant by vegetative means. As little as 0.7g of viable rhizome can give rise to a new plant. See the images below to assist in identifying knotweed rhizomes.
Japanese knotweed stems
Japanese knotweed stems grow to 2-3 metres tall. They’re similar to bamboo with nodes and purple speckles and the leaves shoot out from the nodes in a zig zag pattern. The inside of the stem is hollow. At the mature stage, the stems are hollow and not woody and can be snapped easily to show their hollowness. However, in the winter the stems become brittle, as can be seen from the images below.
Japanese Knotweed Identification Video
We show you how to identify Japanese knotweed by showing you its key identifying features and how it can sometimes be confused with other common plants.
Do you think you can identify Japanese knotweed?
Japanese knotweed can grow in different shapes and forms depending on the season, previous treatments and the surrounding environment. Bonsai growth is completely different from normal growth and this makes identifying Japanese knotweed a challenging prospect which requires a trained eye.
Try out our identification quiz to put your knotweed identification skills to the test!
Other Types of Knotweed
Giant knotweed (Fallopia sachalinensis)
Giant knotweed is a native of South Sakhalin, Honshu (in the north of Japan), Korea, and the Kurile Islands. It is a closely related species to Reynoutria japonica, but less widely distributed outside of the Far East. Both male and female plants have been recorded in Europe and the UK. Although similar in many respects to japonica (cane structure, distinctive ‘zig-zag’ shape of stems, similar growth habit, etc), it grows much taller (4-5 metres or 13-16 feet) and has much larger, elongated leaves. The leaves can grow to around 40cm (16 inches) long and up to 27cm (11 inches) wide.
They are pointed at the tip, somewhat crinkly in appearance and have long white hairs (trichomes) on the underside. The base of the leaves are deeply lobed, forming a heart shape. Growth generally begins later than japonica, usually mid to late spring, and leaf drop generally occurs earlier than japonica in the autumn. Rhizomes are more creamy in colour internally, rather than the distinctive orange of japonica. Creamy-white flowers appear in late summer/early autumn in dense panicles hanging off the stems. The Japanese call Giant knotweed ‘o itadori’, which, with enviable simplicity, means “big strong plant”.
Bohemica (Fallopia x bohemica)
‘Bohemica’ is a hybrid species formed by Japanese knotweed and Giant knotweed. Consequently, it is also known by the name Fallopia japonica var. japonica x Fallopia sachalinensis. For many years, ‘Bohemica’ went unrecognised as a separate species and was only formally classified in 1983. It is widely distributed, with both male and female plants recorded in the UK. It can be variable in habit and it is common to find ‘bohemica’ growing in close proximity to, or amongst, Japanese knotweed. Leaves are larger than Reynoutria japonica, up to 25cm (10 inches) long and 18cm (7 inches) wide, growing in a heart shape. Leaves are usually longer than they are wide, pointed at the tip, slightly crinkled in appearance and darker green than japonica, with short white hairs (trichomes) growing on the veins on the underside – particularly in the early part of the growing season. Veins are usually reddish purple in immature leaves. Growing habit, including stem colour and shape, is extremely similar to japonica. ‘Bohemica’ grows, on average, to a height of 2.5m-3m (8-10 feet), though taller plants up to 4m (13 feet) have been recorded. Rhizomes have a less prominent colour internally than japonica and can be bleached out completely to white. An absence of crowns has been noted during excavations. Creamy-white flowers appear in dense clusters in late summer/early autumn.
Dwarf Japanese knotweed (Fallopia japonica var. Compacta)
Also known as Polygonum reynoutria, Polygonum compactum and Polygonum pictum, ‘Compacta’ is a dwarf form of Japanese knotweed. It reaches only 1m-1.8m (40 inches) in height, and emerges later than standard japonica (usually late spring). It retains the distinctive ‘zig zag’ petiole structure, but the leaves are darker green, more variable in shape, up to 11cm (4 inches) long and up to 10cm (3.5 inches) wide. Leaves have crinkled edges, a leathery texture, reddish veins and are often curled into a concave form. Upright clusters of white or pale pink flowers appear in late summer, which often mature to dark pink or red. Both male and female plants occur in Europe and the UK, though ‘Compacta’ is rare in countries like Germany and the Czech Republic. Dwarf Japanese knotweed is still available to purchase from some nurseries in the US, where it is promoted for its ground cover properties or as a potted plant. Although smaller and less invasive than Japanese knotweed, Dwarf knotweed still retains some of the voracious growing habit of the species. It seems some lessons are slow to learn.
Himalayan knotweed (Persicaria wallichii)
Himalayan knotweed is known by many names, and is referred to in some sources as Polygonum polystachyum, Polygonum wallichii, Persicaria polystachya, Reynoutria polystachya or Aconogonum polystachyum. With its slender, elongated leaves, it bears greater similarity to Giant knotweed and Lesser knotweed, to which it is closely related, and is often mistaken for Lesser knotweed (and occasionally for Himalayan balsam). Native of the Himalayan region from Afghanistan to south-west China, it is one of the least common knotweeds in the UK, though is more prevalent in the southwest of England. It grows quickly to a height of up to 1.8m (6 feet). Stems are usually green (though leaf stems can contain the distinctive knotweed pink) and have the characteristic ‘zig zag’ from node to node. Stems are hairy, and a key identifier of the plant is the brown sheaths that persist at the bases of the leaf stalks. The dark green, alternate, leathery leaves are 10-20cm long (4-8 inches), tapered to a point. Short hairs can often be found on the veins, edges and undersides. Leaf shapes can differ within the species, with leaf bases varying from tapering to the leaf stem to developing a slight heart-shaped lip. White or pale pink flowers bloom from mid summer to late autumn and occur in loose, branched clusters around 20-35cm (8-14 inches) long. Flowers are hermaphrodite (ie contain both male and female parts). Himalayan knotweed is most commonly found in moist soils and poses a significant ecological threat to riparian areas where it can survive flooding and quickly colonise scoured shores and islands when the flood waters recede.
Lesser knotweed (Persicaria campanulata)
Also referred to in some sources as Polygonum campanulatum, Polygonum campanulata or Reynoutria campanulatum, Lesser knotweed is another member of the species that is still actively being sold by garden centres and plant suppliers in both the US and the UK. A native of North India and Southwest China, this knotweed is less invasive than the others but still retains a familiar vigour of growth. Leaf size can be variable, though conforms to the same long shape. Lesser knotweed bears a casual resemblance to Himalayan balsam (Impatiens glandulifera), and its love of moist soil means it is often growing alongside this troublesome plant. Veins on the leaf can sometimes be reddish and the leaves are distinctly grooved in a pattern reminiscent of herring-bone. The undersides of the leaves are much lighter in colour and are felted by small white hairs. Persicaria campanulata grows to a height of around 60-90cm (2-3 feet) and produces flowers mid-summer that remain until the autumn. The flowers are tiny, pale pink or white, and are bell-shaped (hence the name) and produced in clusters on short spikes. Stems are usually clear of foliage for the lower two-thirds of their length and are slightly crooked due to bending at the nodes. The distinctive knotweed ‘zig-zag’ is missing, although leaves are still produced alternate on the stem. This species is less widespread in the UK, though it is more common in parts of Scotland and Northern Ireland.
Plants Mistaken for Japanese Knotweed
Two species that are not knotweeds but can sometimes be mistaken for one by the inexperienced, due to their similar leaf shapes and voracious growing habits, are:
Russian Vine (Fallopia baldschuanica)
Otherwise known as Silvervine, Fleeceflower or more commonly by the name ‘Mile a Minute’. Reynoutria japonica is known to hybridise with this vigorous climber, but the resultant seedlings rarely survive in the wild and possess none of the aggressive attributes of either of its parents. Russian vine is also known by the Latin names Polygonum baldschuanicum and Fallopia aubertii.
Hedge Bindweed (Calystegia sepium)
Also known as Greater Bindweed, Bearbind, Bellbine, Withybind, Devil’s Guts, Hedge-Bell and, most appropriately, Hell Weed. Like knotweed, it gains its strength from an extensive underground stem system and can be extremely difficult to eradicate once it has taken hold. Also, like knotweed, Bindweed can re-establish itself from root fragments. Similar in appearance, though slightly less vigorous in habit, is Field Bindweed (Convolvulus arvensis), otherwise known as Lesser Bindweed.
Part of our Japanese Knotweed Removal Guide. Click to see more answers to your questions.
Knotweed starts out as a reddish/purple shoot sprouting early spring time. The shoot quickly grows, up to 2cms a day to form a hollow stem. The raised nodes along the stem give it an appearance similar to bamboo. As the plant matures during the summer the stem becomes green with numerous small reddish/purple specks. Stems can commonly grow to 2-3m in height. A single plant can sprout several stems in close proximity with each other forming what is known as a stand of knotweed. Unlike some other invasive species, Knotweed isn’t poisonous.
The broad, heart/shield shaped leaves emerge in a zig-zag formation along the branches. The off-white flowers bloom during the summer months and grow in clusters of small spiky stems covered with tiny flowers. As knotweed reaches the end of its yearly lifecycle, the flowers and leaves drop and the stem dies turning to a dry brown cane.
At the base of the stems is a knotty lumpy section called the crown, this is commonly covered with fine brown tendrils giving the crown material a hairy appearance. Close inspection will reveal many small purple shoots on the crown.
The rhizome, buried underground has a woody, knotty appearance and is brown in colour. Scraping back the relatively thin brown outer layers or snapping the rhizome reveals a yellow/orange inner core. Rhizome has a carrot like texture and will tend to break cleanly and requires only a moderate amount of force to snap with your hands. The orange interior is less obvious in fine tendrils at the ends of sections of rhizome making them difficult to identify without larger sections of root nearby. This is problematic during excavations as these sections of rhizome are the most effective at regenerating if left in the ground.
In the UK there are also Giant and Compact Knotweed varieties and a hybrid variety of giant and Japanese knotweed. Giant Knotweed can grow to a height of 5m and has larger leaves, the hybrid will share some of the characteristics of Giant Knotweed and some of Japanese Knotweed although this can vary a bit from plant to plant. The compact knotweed variety grows to only around 1m. In other characteristics such as leaf shape and colour and the appearance of stems these varieties very closely resemble Japanese Knotweed.
A special mention should be made with regards to knotweed which has been treated with herbicide either the following growing season or in the event of a sub-lethal dose in early season treatment. These plants will likely be shrunken and malformed and may appear to be radically different to the normal growth of Japanese Knotweed. In this instance an experienced professional may be required to identify the plants.
Everything you wanted to know about Japanese Knotweed but were too afraid to ask
Japanese Knotweed can be the stuff of nightmares for developers and home owners alike. Not sure if you have a Knotweed problem? Looking for the answers?. This free guide will help educate identify, treat and address the importance of eradicating Japanese Knotweed. Download it now for free!