Typically blooming between late summer and early autumn, Japanese Knotweed is up there as one of the most pervasive property nasties homeowners can face. Even after extensive treatment, this invasive plant can survive for up to twenty years, re-grow at any time, and devalue a property between 5-15% (or more, depending on the scale of the infestation).
Despite its reputation, it is highly common to mistake plants that look like Japanese Knotweed for the real deal. A lot of Japanese Knotweed look-alikes are just benign types of weed which are a lot easier to eradicate.
In this guide, we’ll go through how to identify an actual Japanese Knotweed infestation — and help you ‘weed out’ the real from the fakes.
Japanese knotweed is an invasive and resilient weed that was brought to the UK in the mid 1800’s. The plant has spade-shaped leaves that can grow up to 20cm long, and small, white flowers that bloom in clusters.
During the summer, Japanese Knotweed can grow up to 10 centimetres a day. It has strong roots (known as rhizomes) which can extend up to 3 metres deep into the ground, and start growing again after years of being dormant — making them difficult to remove without heavy machinery.
Untreated Japanese knotweed can also:
- Damage to foundations and walls
- Cause ecological damage
- Grow into (and block) drains
- Reduce biodiversity
- Trap litter, increasing risk of fire and rodent infestation
- Block site lines on roads, railways and buildings
- Cause structural damage to concrete and buildings
While homeowners aren’t legally obliged to treat Japanese Knotweed on their own properties, it’s highly advised you deal with the issue quickly — especially if you’re planning to sell your house fast in the near future.
What’s more, homeowners can be prosecuted for letting Japanese Knotweed spread from their home to public spaces.
Japanese Knotweed is most commonly found on unattended land, or areas with structural weaknesses; such as drains or below-ground gas pipes. Properties that are in close proximity to public watercourses (canals, rivers etc) are more commonly at risk. This is also the case for properties that are close to wide open public spaces, like car parks, railways, or cleared sites.
If the above applies to you, it could be the case that Japanese Knotweed has spread to your property from a bordering infestation.
Bindweed is commonly mistaken for Japanese Knotweed due to its similar heart-shaped leaves. Unlike Japanese Knotweed, Bindweed is a climbing plant that twists around other plants and structures. It also has large pink and white flowers, which can be easily distinguished from the clustered flowers that bloom on Japanese Knotweed.
Because of its perennial root system, Bindweed can live a long time — and is difficult (but not impossible!) to get rid of without professional intervention. With the right treatment, you can resolve the problem within a year.
Russian Vine is biologically the most similar plant to Japanese Knotweed. It has similar shaped leaves, and similar looking flowers. What’s worse, Russian Vine can cross-pollinate with Japanese Knotweed to create a fearsome hybrid plant. The biggest difference is that, like Bindweed, Russian Vine is a climbing plant which doesn’t grow directly upwards like Japanese Knotweed does.
While Russian Vine grows extremely fast, and can quickly suffocate other plants in proximity, it’s a lot less persistent — and can easily be treated at the root.
Broadleaved Dock is part of the same family as Japanese Knotweed, so they share a few key similarities; namely the shape of the leaves and flowers, as well as the speed of growth. However, Broadleaved Dock stems are fluted, as well as being shorter than knotweed plants. The plant itself is also shorter than Japanese Knotweed.
If you’re still unsure, snap open the stems. If they contain a foam-like substance, you can be sure it’s not Japanese Knotweed (which has hollow stems). While Broadleaved Dock is a nuisance, it’s easily eradicated with a few rounds of herbicide.
Himalayan Balsam is a fast-growing, but non-invasive plant. The stems are also hollow with the leaves arranged in a similar way to the Japanese Knotweed, so it’s easy for alarm bells to ring when it’s spotted at the foot of your garden. What’s more, Himalayan Balsam can grow to a similar height — and is also often found near watercourses.
The leaves on a Himalayan Balsam are much longer and thinner than Knotweed leaves, and form large pink hooded flowers (which bloom during the summer).
While you wouldn’t necessarily think of bamboo when you see pictures of Japanese Knotweed, the shoots are incredibly similar — and many early signs of Japanese Knotweed are mistaken for pre-planted Bamboo. Bamboo also grows very quickly, and can grow as tall (sometimes taller) as Japanese Knotweed.
Unlike Japanese Knotweed, Bamboo leaves are long and thin. Bamboo is also a lot stronger, whereas Japanese Knotweed will easily break with force.
Red Bistorts is a popular decorative garden plant, and another close relative of Japanese Knotweed. Like Japanese Knotweed, the hollow stems are separated into nodes; and the leaves are alternately arranged along the stems (though Red Bistorts stems are usually much thinner).
Similar to Bamboo, Red Bistort is usually planted intentionally as an ornamental plant. They don’t spread easily, and the flowers range from pink to reddish-purple.
Houttuynia is commonly mistaken for Japanese Knotweed. Like Japanese Knotweed, this perennial can spread through its rhizomes. It also has heart-shaped leaves (hence the name) which are similar in shape and size to that of the Japanese Knotweed.
Unlike Japanese Knotweed, the Houttuynia doesn’t usually grow past 30 centimetres in height; and has tiny yellow flowers as opposed to white flowers.
Unfortunately, there’s no ‘quick fix’ when it comes to treating Japanese Knotweed. Depending on the scale of the infestation, you may have to get a surveyor round to advise on next steps. Make sure you understand the root of the issue — if the infestation spread to your property from elsewhere, you might not need to be the one to foot the bill.
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