There are various myths about Japanese Knotweed which are incorrect – here are the top 5.

1. Japanese knotweed can grow through concrete

It is often claimed in the media that Japanese knotweed can grow through tarmac and concrete. Knotweed actually can’t do this, but what it will do is exploit any small joints or cracks and weaknesses in tarmac and concrete and grow through them in search of light. The general rule of thumb is that if water can penetrate it, so can Japanese Knotweed.

2. You can kill Japanese knotweed by cutting down the stems and pouring diesel/bleach/glyphosate into i

This will not ultimately kill Knotweed, even if all the above ground growth has gone. Firstly, by cutting the plants down, you are stopping the internal workings of the plant, meaning water and nutrients will not be circulating around the plant – and nor will the chemicals you have applied! DIY treatments often shock the Knotweed into a state of dormancy – giving you the impression it is dead, but once ground conditions improve again, or the ground is disturbed, more often than not, the Knotweed will grow straight back. Japanese Knotweed has been reported to stay dormant for up to 15 years.

DIY treatment can also make it harder for knotweed removal experts to deal with an infestation, as it limits the options available. The other downside to DIY attempts is that they will not be supported by an Insurance Backed Guarantee, (IBG), so if you try to sell or re-mortgage the property, banks and building societies will be unlikely to lend.

3. It is illegal to have Japanese knotweed on your land

There are many laws surrounding knotweed, which can be confusing.

Japanese knotweed is not a notifiable weed nor is it illegal to have it growing on your property as long you don’t allow it to spread onto adjoining land. If this happens, either a civil nuisance claim can be brought against you for allowing the Knotweed to trespass or encroach onto private land, or you may be committing a criminal offence under the Wildlife and Countryside Act 1981 if you have caused Japanese Knotweed to grow in the wild.

4. Japanese knotweed spreads by seed

Every Japanese knotweed plant in the UK is female, meaning that flowers are not pollinated and do not therefore produce seeds. All of the plants in the UK have either been intentionally planted, spread naturally through the underground development of rhizome or have been accidentally moved from one site to another in infested soil.

A piece of rhizome the size of your thumbnail is enough to generate new growth, and as a pioneer species it can survive pretty tough conditions, going on to thrive where other species cannot.

UPDATE 2021 – A male species plant of Japanese Knotweed was found in Southern England in 2021 and research is underway to find out how this male plant arrived and grew in the UK, and the ramifications are huge if the male plant has spread further.

5. Lenders will only accept work and guarantees from PCA members

One of the first questions many of our clients ask is ‘Are you a member of the PCA?’

Many news articles in the media state that mortgage lenders will only accept work completed by a PCA member. This is not the case, as there are many reputable and capable companies who are not members of the PCA but do offer insurance backed guarantees.

Our recommended treatment companies mainly issue guarantees which are underwritten by Lloyd’s, an A-rated insurer and are accepted by most banks and building societies.