Japanese Knotweed Myths, Misconceptions and Facts
There are many misconceptions regarding how one should control Japanese Knotweed and what is 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 starting point, type Japanese Knotweed Services / Eradication / Removal accompanied by the name of any large UK city or region into google and take some time to check out some local contractors’ websites. While some contractors are undoubtedly very professional, ethical, and like ourselves, firm believers in informing customers what Japanese Knotweed can and cannot do, there are others who don’t share the same values. You may have noted the following assertions:
“It will grow through solid concrete”
“It can destabilise foundations”
“Has the potential to cause structural damage”
“Japanese 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”
To make things clear and unequivocal, providing any groundwork/construction works have been completed correctly and to a high standard, it is almost impossible for Japanese Knotweed to grow through a slab of solid concrete, nor will it ‘destabilise solid foundation’s. Furthermore, there have been very few instances whereby the plant has had a dramatic ‘negative effect’ on a solid structure.
True or false?
In some cases, Japanese Knotweed treated with an approved herbicide before it becomes established can have such an impact, it does not re-appear in the following years. However, repeated herbicide application is necessary in the majority of cases. According to conventional wisdom, the longer the plant has been prevalent, the more difficult it will be for the herbicide to penetrate the crowns and 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 Japanese Knotweed via the herbicide method, within one year or growing season.
What is above ground is destroyed by burning. However, the problem lies beneath as 60% of the plant is underground during the height of the season, while new shoots will appear season to season and continue to grow. Burning can help get rid of the dead canes from the previous year’s growth and this is the most prudent way of getting rid of them on site. That’s not the eradication of the knotweed.
As stated above, the root of the problem lies underground, not above ground. The problem cannot be dealt with this way in the long run.
Pulling the plant from the soil will do nothing to eradicate the roots, and inevitably, some part of the rhizome or crown will remain in the soil. The plant will, sooner rather than later, germinate and re-grow, although it may be placed into temporary dormancy as a result.
The presence of Japanese Knotweed on your property is not a crime, however, 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’. Although this is true, allowing Japanese knotweed to spread on neighbouring land could be viewed as a private nuisance as opposed to a statutory nuisance (see our section on Community Protection Notices).
It depends on the circumstances. Under The Environmental Protection Act 1990, any Japanese 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). Using an approved herbicide, letting the plant degrade naturally and burning the material in situ are the most practical and cheapest disposal methods.
Yes, you can, although it goes without saying that you should avoid it once it’s been treated with herbicide! Often called ‘Wild Rhubarb’, the shoots are full of water and have a similar flavour to the Rhubarb sold in supermarkets. Much like Hogweed, it is also an edible, wild plant (during its early stages of development).
That’s wrong. Japanese Knotweed can lie dormant beneath the surface for up to twenty years without giving any indication of its existence. There are numerous qualified ‘theories’ as to why the plant suddenly ‘sprouts’, however, any disturbance of the soil is likely to have a considerable impact. Ever wonder why Japanese Knotweed just appears out of nowhere? The following step should use an approved herbicide that has been tried and tested in the past.