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 stop you from getting a mortgage on your home.
But, do you really know your knotweed from your not-weed?
Japanese knotweed experts from Envrionet say that one in four people mistake knotweed for another common garden plant.
So, if you want to make sure you’ve got your eye on the right plant, here are the five key 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. Free-standing stems
Environet operates a free plant ID service for people who are worried they might have knotweed in their garden, but the data shows that most cases are false alarms.
Only one in six reports to the ID service were knotweed, while one in four reports were actually native bindweed.
Emily Grant, director of operations 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 shaped leaves and grow quickly.
Ms Grant says: ‘Because bindweed is really aggressive and tends to get out of hand people tend to panic and think the worst.’
Knotweed stems (pictured) are tall, straight, and self-supporting. If you see a plant that is winding around something else it is definitely not knotweed
However, the easiest way to tell these two plants apart is to look at the stems.
Ms Grant said: ‘Knotweed is self-supporting, so it will always be standing upright.’
Knotweed stems grow straight and tall, almost like bamboo, and are pale green with pinkish-purple splotches.
Bindweed, on the other hand, has to wrap itself around other objects and plants like a vine to climb up.
‘So, if you come across a plant and it’s wrapping itself around something else, then it’s almost certainly not knotweed,’ Ms Grant added.
Japanese knotweed (left) can often be mistaken for bindweed (middle top), 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.
Ms Grant explained: ‘The leaves of bindweed are heart-shaped, so where the stem meets the leaf, it dips down into a heart shape.
‘For Japanese knotweed, where the stem meets the leaf it is very flat.’
Knotweed leaves are bright green, broad, and shovel-shaped.
Another important sign is that 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 you are dealing with knotweed.
Knotweed leaves (pictured) are shovel-shaped and are arranged in an alternating zig-zag pattern on the stem
3. Red shoots
At this time of year, there won’t be a lot of the plant to see since Japanese knotweed is a perennial which dies back each winter.
However, in the next few weeks, new shoots will begin to appear.
These shoots are extremely distinctive with their bright red colouration and are often compared to asparagus.
Knotweed shoots are much more red than the fully grown plant so this can be a good time to spot it pushing up.
Ms Grant says that she and the team are now on ‘high alert’ for the emergence of new shoots.
‘It can grow up to 10cm in height per day, so you can literally see it growing from one day to the next, whereas our native plants are hardly growing by comparison,’ she said.
At the start of spring, knotweed will begin to produce small red shoots that look similar to asparagus stems
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 bunches of small, creamy white flowers.
Some sub-species of knotweed such as the dwarf Japanese knotweed or the Himalayan knotweed can also have pale pink flowers.
However, these species are much less aggressive and are far less common in the UK.
No matter their colour, the flowers should still be easily distinguished from those of bindweed.
Bindweed flowers are large, white, and trumpet-shaped, growing individually rather than in clusters.
Knotweed flowers begin to emerge in late summer and early autumn.
Unfortunately, flowering is usually a sign that the plant is well-established and may be very difficult to remove.
Knotweed flowers (pictured) are small and creamy white. They grow in dense clusters along the stem and bloom in late summer to early autumn
Bindweed flowers (pictured) are easily distinguished from knotweed since they are large and trumpet-shaped
5. Orange roots
Knotweed is what Ms Grant describes as an ‘iceberg plant’, meaning the majority of the plant structure is actually below ground.
‘What you see at the top is nothing compared to what is going on under the ground,’ 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 fast without anyone even noticing.
However, these distinctive roots also make knotweed easy to identify.
One of knotweed’s most distinguishable features is the large network of rhizomes which grows underground. These are easily snapped and are bright orange on the inside like a carrot
Ms Grant said: ‘The most distinctive part about Japanese knotweed roots is that they are bright orange inside and snap really easily.
‘We say that if you find something that looks like a carrot but isn’t a carrot, it’s probably Japanese knotweed.’
While some other plants can also have orange roots, these will not break as easily.
Knotweed rhizomes snap into tiny pieces because a full plant can grow from a piece the size of a fingernail.
When the soil is disturbed, this means that the rhizomes are easily broken and spread around, creating many new plants.