Is Japanese Knotweed Poisonous or Harmless?
Despite being regarded as the UK’s most aggressive and destructive non-native weed, many uncertainties still exist around Japanese knotweed. And one of the most common questions people ask is whether Japanese knotweed is poisonous.
Japanese knotweed has gained a nasty reputation as a wild, invasive species with an alarming growth rate. When left uncontrolled, this troublesome super-spreader can quickly take over large swathes of land, disrupt ecosystems, and damage solid structures including buildings.
This blog will examine the threat Japanese knotweed poses to humans and pets as a wild, perennial plant, and how to react should you encounter it. Meanwhile, if you discover Japanese knotweed on your property or land, the most effective way to stop it from spreading is to remove it completely. Given the complexities involved with safe removal, it’s better to use a specialist Japanese knotweed removal company to do the work for you. Removing knotweed without expert knowledge carries a serious risk of spreading the plant to previously unaffected areas and making the problem worse.
Is Japanese Knotweed Poisonous to Humans, Dogs, and Cats?
No, Japanese knotweed is not poisonous or harmful to humans, dogs, cats, or other animals in general. Confusion may arise due to the similarity of its name to giant hogweed, which is another non-native species that is particularly harmful and can cause severe burns and blistering when in contact with the skin.
Many plants, such as lilies and tulips, can cause harm to dogs, cats, and pets due to their toxic nature, but that list does not include Japanese knotweed. Domestic animals are unlikely to take a bite out of knotweed or attempt to eat it. If they do, they shouldn’t suffer any harmful effects as a result.
Even though Japanese knotweed does not contain any poisonous elements, you should always exercise extreme caution around the plant because it can be so easily and inadvertently spread. All it takes is one tiny fragment of knotweed crown or rhizome (root) to set off new growth in a previously uncontaminated location.
Is it Dangerous to Touch Japanese Knotweed?
No, it is safe to touch Japanese knotweed and you should experience no reaction to handling the invasive species with your bare skin.
There are more than 50 invasive plant species listed in the Wildlife and Countryside Act 1981 and it is an offence to plant or cause any of these to grow in the wild. Of these, only giant hogweed is considered ‘dangerous’ as it poses a genuine public health and safety risk, while Japanese knotweed does not.
That said, it’s advisable to wear gloves, long-sleeved clothing, and trousers when around Japanese knotweed to minimise contact with the plant. Even though knotweed isn’t poisonous, any scratches from its stem or leaves could potentially irritate sensitive skin, especially for people with pre-existing skin conditions.
Does Japanese Knotweed Cause a Rash?
Under normal circumstances, Japanese knotweed should not cause any rash or irritation to bare skin upon contact. However, people with allergies or skin of a sensitive nature could experience an adverse reaction when they come into contact with a wide variety of plants, including Japanese knotweed.
While Japanese knotweed is generally harmless to human touch, it is often confused for giant hogweed which can seriously damage skin and even cause blindness. Therefore, it is essential to positively identify Japanese knotweed before you handle the plant. It’s always best to wear a protective layer of clothing, especially when handling plants you’re unsure of.
Is Japanese Knotweed edible?
Yes, Japanese knotweed is edible. It has a tangy flavour similar to rhubarb and can be used in a range of recipes such as deserts, crumbles and chutneys, or even for making beer.
People in Japan often use knotweed in their cooking as their tender springtime stems are popular in stir-fry dishes. However, as the plant matures the stems become tough and hard to chew, causing abrasions to the inside of the mouth.
Not only is knotweed used in cooking, but it is also believed to have health benefits and is used in traditional Japanese and Chinese medicine. However, anyone foraging for Japanese knotweed should exercise extreme care and adhere to the law. It remains an offence to plant or spread knotweed in the wild and the penalties include fines or even imprisonment. Therefore, you must fully understand the legalities around Japanese knotweed before you start foraging for it.
How does Japanese Knotweed Spread?
If it wasn’t so damaging to the environment and structures, Japanese knotweed could be considered an impressive plant. Only the female species was introduced to Britain in the mid-1800s, so it almost never produces seedlings for reproduction because it doesn’t have a male plant to fertilise with. As a result, the only way this foreign invader can spread is vegetatively from fragments of its rhizome (roots) or cuttings being moved from one location to another, And it does this rather successfully when left uncontrolled.
The roots of Japanese knotweed can grow up to 20cm per day, while the plant can also reach 10 feet in height. This rapid and relentless growth means it spreads extremely quickly and takes little time to conquer land at the expense of native species and habitats.
Japanese knotweed remains dormant in the winter but spreads incredibly quickly during the height of the growing season. Its roots account for around 60% of the plant, making removal extremely difficult and best left to the experts. Not only that, but knotweed rhizomes can remain dormant in the ground in the harshest of conditions for 10 years or more. This is particularly problematic if the ground it sits in is disturbed or moved as it could reawaken the plant and cause rapid new growth. For this reason, housing developers working on new plots often install protective membranes to hinder the spread of knotweed. However, the best way to deal with knotweed is to remove it from your land completely using a professional knotweed removal company.
If left untreated, knotweed can also damage property and grow through any existing cracks in concrete and brickwork. This can cause serious problems when selling a home if knotweed is present. In these cases, you’ll need to prove you have a management plan in place in order to satisfy mortgage lenders and home buyers.
How Do You Remove Japanese Knotweed?
You must take extreme care to remove and dispose of Japanese knotweed. You are not legally required to remove Japanese knotweed from your land unless it’s causing a nuisance to a neighbouring property. However, you can be prosecuted for allowing it to spread into the wild where it can quickly overtake natural habitats, displace native plant species, and lead to soil erosion.
Japanese knotweed treatment and removal basically involves excavating the land and soil itself, and disposing of it properly. However, the way it is handled and dealt with depends on the land you’re working with This is essential to ensure nothing of the plant is left behind as even a tiny piece of root fragment has the potential to regenerate and regrow over time, causing further damage to land and property.
You will need extensive knowledge and experience of Japanese knotweed removal and disposal to get rid of it legally and successfully. You’ll also need to be licenced to dispose of it. However, it is advisable to enlist the services of a professional knotweed removal company with expertise in the treatment, removal, and disposal of this aggressive and invasive species.
Need Help with Japanese Knotweed Identification and Removal?
Are you concerned about Japanese knotweed on your land? The quicker you act the better it will be. Japanese Knotweed Specialists will devise a plan for the removal and disposal of knotweed from your premises and provide a 5 or 10-year insurance-backed guarantee. Stop the spread of Japanese knotweed by arranging a survey today.