Do YOU know how to recognize it? One in four people consider Japanese knotweed to be harmless plants in their garden. These are the five most important signs to look out for
Discovering a Japanese knotweed infestation is every homeowner’s worst nightmare.
The invasive plant is expensive to remove, can grow through walls and can even prevent you from getting a mortgage on your home.
But do you really know your knotweed from your non-weeds?
Japanese knotweed experts from Envrionet say one in four people mistakes knotweed for another common garden plant.
So if you want to make sure you have the right plant in mind, here are the five most important signs to look out for.
Japanese knotweed can be an expensive and destructive force in your garden, but many people struggle to identify this invasive plant
1. Freestanding stems
Environet offers a free plant identification service for people concerned that there is knotweed in their garden, but data shows that in most cases this is a false alarm.
Only one in six reports to the ID service concerned knotweed, while one in four reports actually concerned native bindweed.
Emily Grant, operations director at Environet, told MailOnline that this is by far the most common plant to be mistaken for knotweed.
Knotweed and bindweed both have somewhat similar leaves and grow quickly.
Ms Grant says: ‘Because bindweed is very aggressive and tends to get out of control, people often panic and think the worst.’
Knotweed stems (photo) are long, straight and self-supporting. If you see a plant wriggling around something else, it is definitely not knotweed
However, the easiest way to tell these two plants apart is to look at the stems.
Mrs Grant said: ‘Knotweed is self-supporting so will always remain upright.’
Knotted stems grow straight and tall, almost like bamboo, and are light green with pinkish-purple spots.
Bindweed, on the other hand, must wrap itself like a vine around other objects and plants to climb up.
“So if you come across a plant wrapping itself around something else, it’s almost certainly not knotweed,” Ms Grant added.
Japanese knotweed (left) can often be mistaken for bindweed (top center), dogwood (top right) or lilac (bottom right). But by looking at the stems you can easily tell these plants apart
2. Spade-shaped leaves
Although knotweed and its similar species have similar leaves, there are differences you can learn to recognize.
Mrs Grant explains: ‘The leaves of bindweed are heart-shaped, so where the stem meets the leaf it tapers down into a heart shape.
‘The stem and leaf of Japanese knotweed are very flat.’
Knotweed leaves are bright green, wide and scoop-shaped.
Another important sign is that knotweed’s leaves are arranged in a distinctive ‘zigzag’ pattern along the stem.
Ms Grant says this distinctive leaf pattern is a good indication that you are dealing with knotweed.
Knotted leaves (photo) are scoop-shaped and arranged in an alternating zigzag pattern on the stem
3. Red shoots
Not much of the plant will be visible at this time of year as Japanese knotweed is a perennial that dies every winter.
However, new shoots will appear in the coming weeks.
These shoots are distinguished by their bright red color and are often compared to asparagus.
Knotted shoots are much redder than the mature plant, so this may be a good time to see if it emerges.
Ms Grant says she and the team are now ‘very alert’ to the emergence of new shoots.
“It can grow up to 10cm tall in a day, so you can literally watch it grow overnight, while our native plants barely grow in comparison,” she said.
At the beginning of spring, knotweed begins to produce small red shoots that resemble asparagus stalks
4. Small white flowers
In summer, you can easily tell the difference between knotweed and native plants by looking at the flowers.
Knotweed has very striking clusters of small, creamy white flowers.
Some subspecies of knotweed, such as Japanese dwarf knotweed or Himalayan knotweed, may also have pale pink flowers.
However, these species are much less aggressive and much less common in Britain.
Regardless of their color, the flowers should still be easily distinguishable from those of the bindweed.
The flowers of the bindweed are large, white and trumpet-shaped and grow singly rather than in clusters.
Knotweed flowers appear 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 (photo) are small and creamy white. They grow in dense clusters along the stem and bloom in late summer to early fall
Flowers of bindweed (photo) are easy to distinguish from knotweed, as they are large and trumpet-shaped
5. Orange carrots
Knotweed is what Ms Grant describes as an ‘iceberg plant’, meaning most of the plant structure is actually underground.
“What you see at the top is nothing compared to what’s happening underground,” Ms Grant said.
Knotweed has a very large network of creeping ‘rhizomes’: underground stems that can produce new shoots and store nutrients.
It is these rhizomes that allow the plant to spread so quickly without anyone noticing.
However, these distinctive roots also make knotweed easy to identify.
One of the most striking features of knotweed is the large network of rhizomes that grow underground. These are easy to break and are bright orange inside, just like a carrot
Mrs Grant said: ‘The most striking thing about the roots of Japanese knotweed is that they are bright orange inside and break very easily.
“We say if you find something that looks like a carrot but it’s not a carrot, it’s probably Japanese knotweed.”
Although some other plants may also have orange roots, these will not break as easily.
Knotweed rhizomes break into small pieces because an entire plant can grow from a piece the size of a fingernail.
When the soil is disturbed it means that the rhizomes are easily broken off and spread, creating many new plants.