Read through our comprehensive Japanese knotweed identification guide below. If you’re still not sure, watch our Identification video, get our Quick Digital ID Guide, or send us your pictures, and we’ll tell you for free if it’s knotweed.
Japanese knotweed (Reynoutria japonica syn. Japan’s Fallopia It used to be admired for its beauty, durability, and ability to grow back, but now it is generally seen as a pest species that eats native plants and damages buildings.
From spring to fall, the pictures on the right will help you tell Japanese knotweed from other plants by their most noticeable traits.
Japanese knotweed is an invasive plant that can cause extensive damage to property. Learning how to identify it correctly is key to effective management This article explores the key traits that enable positive identification of Japanese knotweed throughout the year
5 Distinctive Features of Japanese Knotweed
Japanese knotweed has several recognizable features that set it apart from other plants. Watch for:
Spade-Shaped Leaves
The leaves are a clear identifier They have a characteristic spade or shield shape with a squarish base and pointed tip The leaves alternate along zig-zagging stems. When mature, they are bright green and around 6 inches long.
Zigzag Stems
The stems resemble bamboo canes with segments and pronounced nodes. They are green with purple speckles and hollow inside. Stems emerge from the ground in spring and grow rapidly upward in a zigzag pattern, reaching heights over 10 feet.
Orange-Tinged Roots
Underground rhizome roots are one of the most distinctive parts of knotweed. They spread out from the plant and are dark brown externally with a bright orange center when snapped.
Creamy White Flowers
Small greenish-white flowers emerge in late summer in clustered spikes near the leaf joints. They provide an abundance of nectar for pollinators before the plant dies back for winter.
Dead Winter Canes
After frosts, knotweed dies back, leaving tall bare canes that are brown and brittle. These persist through winter until new growth emerges again in spring.
Changes in Appearance Through the Seasons
While Japanese knotweed exhibits the above traits year-round, its appearance changes with the seasons:
Spring
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Red or purple asparagus-like shoots emerge and grow rapidly upwards.
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Rolled up shoots unfurl into green leaves with red veins.
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Can reach 1 meter in height early in the season.
Summer
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Stems fully extend and reach maximum height of 2-3 meters.
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Leaves are bright green and clearly shield-shaped.
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Begins flowering in late summer with small creamy clusters.
Autumn
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Leaves turn yellow then brown before dropping off.
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Stems become woody and turn brown/red-brown.
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Dieback begins after the first hard frost.
Winter
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Leaves absent and stems reduced to brittle brown canes.
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Visible crowns at ground level and scorched earth patches.
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Easily overlooked when dormant.
Where to Look for Japanese Knotweed
Japanese knotweed can grow virtually anywhere but is most prevalent in:
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Gardens and planted borders
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Along transportation routes like roads and railways
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Riverbanks and watercourses
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Wasteland and neglected areas
It readily invades weakness in the built environment like cracks in concrete, walls, and paving. Knotweed will exploit any opportunity to spread.
Common Lookalikes to Avoid Confusing
Some common plants that get mistaken for Japanese knotweed include:
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Bindweed – A climbing vine with trumpet-shaped flowers
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Russian Vine – A fast-growing climber
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Lilac – Shrub with purple flowers
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Himalayan Balsam – Hollow pink-ribbed stems and helmet-shaped flowers
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Broadleaf Dock – Large green leaves form basal rosette
While these plants share some visual similarities, none display the exact combination of traits that positively identifies Japanese knotweed.
Confirming Identification of Japanese Knotweed
If an unfamiliar plant exhibits some qualities of Japanese knotweed, it’s smart to enlist professional help confirming identification before taking action. Misidentification can lead to unnecessary treatment of benign plants.
Experts offer free image-based knotweed identification services. Send photos of the suspect plant taken from multiple angles and growth stages. Qualified specialists will verify if knotweed is present and advise about appropriate management.
Catching knotweed early before extensive growth or damage sets in greatly improves control prospects. But first, proper recognition of the invasive plant is vital. Understanding the unique features of Japanese knotweed throughout its lifecycle allows accurate identification. Keep this guide handy for distinguishing this troublesome weed from lookalikes. Correct ID sets the stage for successful knotweed removal and protection of your property. Stay vigilant and don’t hesitate to utilize expert assistance for definitive diagnosis.
Frequently Asked Questions About Identifying Japanese Knotweed
What does Japanese knotweed look like in spring?
In early spring, knotweed starts growing rapidly as reddish or purple asparagus-like shoots. By late spring, it can reach over 1 meter high with rolled up shoots unfurling into green leaves marked with red veins.
How can you identify Japanese knotweed in winter?
In winter, identifying knotweed is trickier when the plant lies dormant underground. Look for dead brown canes left standing and crowns at ground level. Also inspect for scorched patches where other plants die off.
Does Japanese knotweed have pink flowers?
The invasive Japanese knotweed has creamy white flowers in late summer. Some less common related species have pinkish flowers but are less widespread in the UK.
What is the difference between bindweed and Japanese knotweed?
Bindweed is a climbing vine with trumpet flowers. Japanese knotweed is an upright free-standing plant with bamboo-like stems and creamy flower spikes. But both have similar heart-shaped leaves that cause confusion.
How deep do the roots of Japanese knotweed grow?
The rhizome root system can extend down up to 3 meters deep and spread out 7 meters horizontally. This extensive underground growth makes removal challenging.
What plants are often mistaken for Japanese knotweed?
Some common lookalikes include bindweed, Russian vine, Himalayan balsam, lilac, broadleaf dock, and bamboo. None display the exact combination of leaf shape, flowering, stem and root traits that positively identifies knotweed.
By familiarizing yourself with the unique characteristics of Japanese knotweed as it progresses through its lifecycle, you can reliably distinguish this damaging invasive plant from lookalike species. Make sure to seek expert assistance if unsure – incorrect identification can be costly. Stay vigilant and activate control efforts promptly once the presence of Japanese knotweed is confirmed on your property.
How deep do Japanese knotweed roots go?
Japanese knotweed spreads from its highly regenerative underground rhizome system. Even though the amount of above-ground growth that can be seen is a good sign, it doesn’t show the whole rhizome system. Japanese knotweed has very bad roots that can go as deep as 3 meters (most often they only go 1 meter). 5-2m) which is what makes it so hard to get rid of.
The plant grows just as quickly above ground, and it can quickly reach two or three meters in height. An old plant that is well-established can grow up to 10 cm a day and can quickly get out of hand. The infestation above ground isn’t too hard to get rid of, but the roots below ground are what really bother people.
Their roots can get too deep for most gardening and digging methods, which is why you should get a professional to take care of the issue. If there is even one rhizome left in the ground, the plant will start to grow again and will take over if nothing is done.
Knotweed rhizome in the ground.
Regrows from tiny fragments.
Where does Japanese knotweed grow?
Japanese knotweed can and will grow pretty much anywhere. It is an amazingly resilient plant that can tolerate extremes in temperature, moisture, and pH. With its energy-packed rhizome system and ability to grow quickly, Japanese knotweed has an edge over many other plants. It can establish itself in places where other plants would not be able to. We’ve seen Japanese knotweed grow in a lot of different places over the last 25 years, such as on beaches, in riverbeds, between rocks, and even in chimneys!
Since its introduction in the 1840s, Japanese knotweed has spread to every corner of the UK. Some places are more badly affected than others. That’s why we made ExposedTM, the Japanese knotweed Heatmap, to keep track of the species’ spread over time.
Japanese knotweed is most commonly found in the following places:
- Residential gardens.
- Roadside verges.
- Railway embankments.
- Riverbanks.