There are many plant species in the UK that are harmful to humans and animals, although not being poisonous, Japanese knotweed can cause house and building damage.
Japanese knotweed and other fast-growing invasive species cause numerous problems. Many of these are harmful to humans and animals, but even non-poisonous plants can cause damage and be costly for home and landowners.
Is Japanese knotweed poisonous to humans?
Japanese knotweed is not poisonous to humans. In fact, it is edible, but it is not recommended you eat the weed raw, as some reports claim the weed can cause irritation to sensitive skin.
The danger of Japanese knotweed doesn’t come from consuming it, but more the effects it can have to your home, land or building if discovered, leading to costly treatment if identified, or costly legal battles if ignored. The risk with Japanese knotweed comes with its ability to grow from even the smallest piece of stem.
Japanese Knotweed Damage
Japanese knotweed shoots can grow up to 3 metres high through your plumbing, building foundations, and driveways. It outcompetes native vegetation and can also lead to erosion, causing long term flooding issues.
Its ability to exploit existing weaknesses in properties as well as underground systems, walls and building foundations mean repair work can range into the thousands. With its advanced root network, the rhizomes grow through any structure.
Your mortgage and house price can also suffer. Legally, Japanese knotweed must be disclosed to buyers and banks. Many lenders have been reluctant to approve mortgages on properties with a history of knotweed without a solid Japanese knotweed treatment plan or 10 Year Insurance Backed Guarantee.
The Wildlife and Countryside Act prohibits planting Japanese knotweed or disposing of cuttings in an irresponsible manner that might let it grow back. Japanese knotweed can grow back, from cuttings as small as 2mm. This makes home knotweed treatment almost impossible without risk of costly fines and criminal action.
How does Japanese knotweed spread?
Not only can it damage and destroy hard surfaces, such as tarmac, concrete and brick walls, the plant grows so quickly and spreads so easily, it can deprive native plants of nutrients and sunlight, causing them to die. Having evolved on the harsh conditions of the sides of volcanoes in Japan, its growth rate is legendary.
In summer months the plant can grow up to 10cm a day, reaching a height of around 7 metres.
Touching Japanese knotweed is not advised under any circumstances, as this can contribute to the spread of the weed. If you have Japanese knotweed on your property and you allow it to spread to a neighbours land, you can face fines of up to £2,500.
Japanese knotweed is the UK’s most aggressive invasive weed. Left untreated, it will spread and spread. It is a criminal offence to allow the weed to spread from your land to a neighbouring property.
Is Japanese knotweed poisonous to dogs and cats?
Dogs and cats have different digestive systems to those of humans and standard livestock animals. Reports vary as to the effects of Japanese knotweed consumption on dogs and cats, with some owners claiming the knotweed has harmed their pet and others saying the knotweed has actually improved their health.
More research is required to validate the effects of knotweed consumption on dogs and cats. In the meantime, it is advised you do not let your pets consume the weed.
Is Japanese knotweed poisonous to livestock?
Your livestock can also safely eat Japanese knotweed. Many reports indicate horses, cows, and goats will readily eat the broad leaves when available without adverse effects.