Japanese Knotweed! NIGHTMARE and EXPENSIVE!

by Pete
(North East Lincolnshire)

Just a quick message to all who are thinking about doing a self build and looking for a plot of land! Before you buy the land, make sure the surveyor checks for signs of Japanese Knotweed, or other such weeds that are VERY VERY VERY costly to remove from the land! We have approximately 200m2 of our 650m2 plot that's infested with Japanese Knotweed. Have been quoted £20k - 50k for immediate removal. Madness, as that will increase build cost by at least a third!

Obviously if you have 2 - 3 years to wait, you can use a herbicide method which comes in at a real fraction of that cost. My planning permission runs out on August 20th this year. Thinking I may let the planning lapse take the 3 year herbicide option and then develop!

If anyone has had any such experiences would love to hear from you, as ANY advice or contacts would be gratefully accepted.


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Comments for Japanese Knotweed! NIGHTMARE and EXPENSIVE!

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Jul 04, 2015
JKW problem
by: Anonymous

Hi - Try this:


I read the article, and there are some developments coming through for natural bug control of the species. May be worth investigating if it's now an option.

Jul 04, 2015
Japanese knotweed
by: Anonymous

We had Japanese knotweed in our garden and spent a considerable few hours digging it out and conscientiously burning the roots - 20 yrs on, we had one piece this year, and that's the first for 18 years, so if you don't mind some hard graft, then you could sort it much faster....

Aug 19, 2011
Thanks for your commEnt bill
by: Anonymous

Bill, thanks for your feedback! Yeah it's a pain that Jkw! Had first course of spray, and going to treat again before end of growing season!

We're putting land up for auction, but new owners will be made aware of Jkw!

Anyway thanks again and good look killing the evil weed!


Aug 15, 2011
by: Bill

hi Pete,
We have 40m2 of JKW in a corner of our plot, thankfully not 200m2, but it's difficult to get at amongst 12 foot blackthorn scrub. I have just inspected the site following the second glyphosate (agricultural strength) application, sprayed on 20th July). Following the first dose in late May, a few fronds/leaves had started poking through again and this 2nd spray seems to have nailed them. I will check in Sept and spray again then if needs be (poss getting a bit late but it's cheap enough if you DIY). So far, I am delighted with the result though expect I may have to revisit for a spray or two next year.
As far as your PP expiry is concerned, you have to do a very modest amount of work to establish the build as "started", as I understand it. A stand-pipe or beginnings of a bit of trench work has been suggested to me in the past to validate the PP.
Best of luck.

Jul 25, 2011
Update on JKW on my land!
by: Pete

Thanks for the comments you've given. Quick update on how things are going.

Well after contacting a number of JKW removal companies, i've managed to get a company down to around the £13,000 mark to remove and remediate the land followed by a herbecide treatment of around £270 a go.

However, I have been quoted around £100 per herbicide visit by other companies, so I am thinking that I will get the main removal done for £13,000 and then following herbicide visits done at £100. This will keep the cost right down and probably come in around the £14,000 mark. Damn sight better than the £20k - £50k i was getting originally.

Furthermore I've still got other companies quoting on the removal based on my £13,000 quote, so I am expecting some lower quotes. If I can get to the £10,000 mark the build should easily absorb the extra cost as long as I do some of the work myself.

My advice to people is if you get JKW on your land, shop around, haggle with them, and just try get them to compete against each others quotes.

You can even decide to do the herbicide treatment yourselves, as they only use the industrial version of Round-Up Herbicide that is available online if you want to go down that route. To be honest you could probably do the treatment for a few £100, once the main JKW has been removed.

Most have estimated full eradication after two years, but you may get the odd re-sprout that needs herbicide for upto 5 years, but you just need to keep on top of it until it is fully killed off.

Anyway, hope this helps people out there, and I would recommend the InvasivePlantCompany, Guy called Brad, who's offered me advice and has been pretty sound considering this extra cost may make or break the project.

Regards Pete

Jul 19, 2011
JK Treatment
by: Soilutions Ltd

You may have already found that a lot companies out there deal with Jap Knot. We don't ourselves, however some like Dunton Environnmental offer a machine which cuts and kill the roots and allows the soil to be re-used.

Good luck

Jul 16, 2011
Highly Invasive
by: James

Hi Pete,

Thank you for bringing that one up. Japanese Knotweed is indeed a huge problem. It is the most invasive species of plant in the UK and any soil contaminated with it is classed as controlled waste. Hence the price tag for removal.

Less than a gram of root matter can produce a plant which grows at a rate of 2cm a day and worse still, through concrete and masonry!

As far as we know there are really only the two options of lengthy herbicide treatment or plant and ground removal that you have mentioned. I think you are stuck between a rock and hard place here Pete.

If you haven't already visited them, the Environment Agency has produced a code of practice for dealing with Japanese Knotweed,


and the Devon Knotweed Forum has a lot of information and advice.


Good luck with it and let us know how you get on.

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