The Knotweed Myths, Untruths & Misconceptions

Get in touch to arrange a site visit

Knotweed Myths, Misconceptions and Facts

Knotweed Myths, Misconceptions and Facts

There are many mistaken notion's as to how you can eradicate Japanese Knotweed and what is really the best course of action to take. Pouring salt, diesel, caustic soda, turpentine, fairy liquid on the plant or into the ground are just some of the common fallacies which appear to have gathered momentum over the years, whilst others may be considered as a mixture of being quite innovative, yet some would say, rather ridiculous.

As a starter, type ‘Japanese Knotweed Services / Eradication / Removal’ along with any name of a large city or region located within the UK into google and take a few minutes to check out some of your local contractor’s websites. Whilst some contractors are undoubtedly very professional, ethical and like ourselves, firm believers in telling the public exactly what Knotweed can & can’t do, there are sadly others who don’t share the same values. You may have noted assertions similar to the following:-

“It will grow through solid concrete”

“It can destabilise foundations”

“Has the potential to cause structural damage”

“Knotweed can damage buildings especially if left to grow unhindered for a number of years”

“This invasive plant can have such a dramatic effect on structures, foundations & concrete”

Just to make things clear and unequivocal, in simple terms providing any previous groundwork / construction works have been completed to a sufficient standard, Knotweed will not grow 'through solid concrete’, it will not destabilise solid foundations, it will not cause structural damage, it will not 'damage buildings' and it won’t have a dramatic effect on any ‘solid structure’. In truth, these claims are misleading to say the least and in some cases, false.


“You can get rid of Knotweed in one year”

In some cases, treating newly emerging & unestablished Knotweed with an approved herbicide, MAY have such an impact, that it does not re-appear in the following years. However in the majority of cases, a repeated herbicide application programme over several years will be required. Conventional wisdom is that the longer the plant has been prevalent, the more difficult it will be for the herbicide to penetrate the crowns & rhizomes (root system). Whilst one or two precise applications of herbicide will cause disruption to the plants growth cycle, do not accept any assurances or guarantees from anyone, who claim to be equipped to eradicate any Knotweed via the herbicide method, within one year or growing season.

"Burning Knotweed with Diesel will kill it!"

Burning will destroy whatever is above ground. The problem however, is what lies beneath as approximately 60% of the plant in the height of the growing season is underground, whilst new shoots will emerge from season to season and will continue to grow. Burning will help in order to dispose of the ‘dead canes’ from previous year’s growth and this is the most prudent method of disposal on site. Not eradication!

"If you cut it straight away early in the season, you can kill it that way."

As stated above, the source of the problem lies beneath the ground, not above. This will do nothing to eradicate the plant in the long term.

"The best thing to do is pull it from the ground and pour fairly liquid or salt into the soil."

Pulling the plant from the ground will do nothing to achieve eradication and inevitably, will leave some portion of the rhizome or crown (the root system) within the soil. Over time, although doing so may reduce the plant into temporary dormancy it will sooner rather than later, germinate and regrowth will occur.

"It’s illegal to have Japanese Knotweed growing on your property."

Having Knotweed on your property is not an offence. Under Section 14 (2) (a) of the Wildlife & Countryside Act 1981, it is an offence to ‘plant or otherwise cause Japanese knotweed to grow in the wild’. In spite of this, allowing Japanese knotweed to spread onto neighbouring land could be considered to be a private nuisance as opposed to a statutory nuisance (see our section on Community Protection Notices).

"Japanese Knotweed is classed as contaminated waste and must be taken to landfill."

Dependent on the circumstances. Under The Environmental Protection Act 1990, any Knotweed treated with herbicide and / or removed from its original site must be disposed of appropriately at a licensed landfill designated by the local authority (in doing so, a waste carriers license must be held). The most practical and cheapest means of disposal is to treat with an approved herbicide, leave the plant degrade naturally and to burn the material in situ.

"You can eat Japanese Knotweed!"

Yes you can, although it goes without saying, best to avoid once it’s been treated with herbicide! Often called ‘Wild Rhubarb’, the shoots contain water and are similar in taste to the Rhubarb sold commercially in supermarkets. Just like Hogweed it’s another edible plant (during the early stages of its growth cycle) that grows wild throughout the UK.

"If it’s only just emerged, it means its new and can be treated easily."

Wrong. Japanese Knotweed material can lay dormant beneath the surface for up to 20 or so years without any indication of its existence. There appear to be no shortage of qualified ‘theories’ as to why the plant suddenly ‘sprouts’, however any disturbance of the soil is likely to have a considerable impact. Ever wondered why Knotweed simply appears out of nowhere? The subsequent treatment should be the same tried and tested methods using an approved herbicide.