Knotweed - more than 7m and with treatment plan

[NervousBuyer2021]

So. Having walked away from one house after a bad survey (and seller not willing to work with us to deal with any of the issues) we’ve found what is the perfect house for us, in the perfect location for us...with a small patch of knotweed at the back of the garden.

It’s more than 7m from the house, there is also a small bit in a neighbour’s garden and the seller has already started treatment with herbicide through an approved contractor.

We’ve spoken to the contractor doing the treatment and he’s been very reassuring. He has looked in all neighbouring properties and only found it in two, both being treated and they’ll continue to survey neighbouring gardens and ours for 5 years.

We want to go back and ask him if a quicker (and maybe more effective?) treatment is possible, some kind of excavation. That would give us full use of the garden much quicker as otherwise the treatment takes up to 5 years. We’ll still have plenty of garden but will have to fence off the knotweed bit to make sure it’s not disturbed and able to spread as a result while the herbicide treatment is ongoing.

Wondering if anyone has been through the herbicide treatment programme and had success?

Also wondering if we are naive to think that this all sounds reasonable...we know it’s not ideal but it seems to be possible to sort?

Yes that seems to be an issue alright - there is an industry around treating this particular plant and certification from an approved supplier is needed for mortgage approval so those expert companies are part of building its reputation.

Just updating in case anyone is looking at this thread when they find themselves in this situation down the line. I've spoken to the contractor provding the herbicide treatment.

Their view is that herbicide is very effective as a treatment in terms of knocking back the plant and limiting its spread and that it generally takes 3-4 years of treatment before you will stop seeing any new growth. However the root network is likely to be dormant rather than dead following that treatment and future digging of the garden e.g. extension, landscaping, is quite likely to disturb the root network and lead to it coming back. Or, even if nothing disturbs it, it would quite possibly start to grow again in 10-20 years.

Also 7m is very conservative and the roots are more likely to be 2m or at most 3m from the plant.

Excavation is a much better solution but obviously very expensive and a huge and messy job.

The main issue for us is the risk that the plant pops up again within 7m of our property either due to landscaping or just coming out of dormancy...not worried that the plant will eat our house, but worried that someone in the future will be unable to get a mortgage on it for that reason and we'd be limited to cash buyers.

Still mulling it all over and keeping an eye on other suitable houses coming up. And we've asked the estate agent whether a more permanent solution such as excavation was considered for the knotweed.