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Discovering an infestation of Japanese knotweed is every homeowner’s worst nightmare.
The invasive plant is expensive to remove, can grow through walls, and may even prevent you from getting a mortgage on your home.
But do you really know your knotweed from your non-weed?
Japanese knotweed experts at Envrionet say that one in four people confuse knotweed with another common garden plant.
So if you want to make sure you’ve got your eye on the right plant, here are five key signs to look out for.
Japanese knotweed can be a costly and destructive force in your garden, but many people struggle to identify this invasive plant.
1. Independent stems
Environet operates a free plant identification service for people who fear they have knotweed in their garden, but data shows that most cases are false alarms.
Only one in six reports to the identification service was native creeper, while one in four reports was actually native creeper.
Emily Grant, operations director at Environet, told MailOnline that this is by far the most common plant to be confused with knotweed.
Both knotweed and bindweed have somewhat similar shaped leaves and grow quickly.
Mrs Grant says: “As the vine is very aggressive and tends to get out of control, people tend to panic and think the worst.”
Knotweed stems (pictured) are tall, straight and self-supporting. If you see a plant that is wrapped around something else, it is definitely not gnarled.
However, the easiest way to tell these two plants apart is to look at the stems.
Mrs Grant said: “Knotweed is self-sustaining so it will always be standing.”
Knotweed stems grow straight and tall, almost like bamboo, and are pale green with pinkish-purple spots.
Bindweed, on the other hand, has to wrap itself around other objects and plants like a climbing vine.
“So if you come across a plant that is wrapping around something else, it’s almost certainly not a knotweed,” Ms Grant added.
Japanese knotweed (left) can often be confused with bindweed (top middle), dogwood (top right), or lilac (bottom right). But looking at the stems can be an easy way to tell these plants apart.
2. Shovel-shaped leaves
Although knotweed and its lookalikes have similarly shaped leaves, there are differences that you can learn to spot.
Mrs Grant explained: ‘The leaves of the vine are heart-shaped, so where the stem meets the leaf, it sinks down to form a heart.
“In the case of Japanese knotweed, the area where the stem meets the leaf is very flat.”
Knotweed leaves are bright green, broad, and spade-shaped.
Another important sign is that the knotweed leaves are arranged in a distinctive “zig-zag” pattern along the stem.
Ms Grant says this distinctive leaf pattern is a good indication that these are knotweed.
Knotweed leaves (pictured) are spade-shaped and arranged in an alternating zig-zag pattern on the stem.
3. Red shoots
At this time of year, there won’t be much plant to see, as Japanese knotweed is a perennial that dies back each winter.
However, in the coming weeks new shoots will begin to appear.
These shoots stand out for their bright red color and are often compared to asparagus.
Knotweed shoots are much redder than the fully grown plant, so this may be a good time to spot it pushing up.
Ms Grant says she and the team are now on “high alert” for new outbreaks.
“It can grow up to 10cm tall per day, so you can literally watch it grow overnight, while our native plants barely grow in comparison,” he said.
In early spring, knotweed will begin to produce small red shoots that look like asparagus stalks.
4. Small white flowers
In the summer, an easy way to tell the difference between knotweed and native plants is to look at the flowers.
Knotweed has very distinctive clusters of small, creamy white flowers.
Some knotweed subspecies, such as dwarf Japanese knotweed or Himalayan knotweed, may also have pale pink flowers.
However, these species are much less aggressive and much less common in the UK.
Regardless of color, the flowers should be easily distinguished from those of the vine.
The flowers of the vine are large, white, and trumpet-shaped and grow singly rather than in clusters.
Knotweed flowers begin to emerge in late summer and early fall.
Unfortunately, flowering is usually a sign that the plant is well established and can be very difficult to remove.
Knotweed flowers (pictured) are small and creamy white. They grow in dense clusters along the stem and bloom from late summer to early fall.
Bindweed flowers (pictured) are easily distinguished from knotweed flowers because they are large and trumpet-shaped.
5. Orange roots
Knotweed is what Ms Grant describes as an “iceberg plant”, meaning that most of the plant’s structure is actually underground.
“What you see above is nothing compared to what happens underground,” Ms Grant said.
Knotweed has a very large network of creeping ‘rhizomes’ – underground stems capable of producing new shoots and storing nutrients.
It is these rhizomes that allow the plant to spread so quickly without anyone noticing.
However, these distinctive roots also make the knot easy to identify.
One of the knotweed’s most distinctive features is the large network of rhizomes that grow underground. They break easily and are bright orange inside like a carrot.
Ms Grant said: “The most distinctive part of Japanese knotweed roots is that they are bright orange inside and break very easily.
“We say if you find something that looks like a carrot but isn’t, it’s probably Japanese knotweed.”
While some other plants may also have orange roots, these will not break as easily.
Knotweed rhizomes are broken into small pieces because an entire plant can grow from a piece the size of a fingernail.
When the soil is disturbed, this means that the rhizomes break off and spread easily, creating many new plants.