Help! Japanese knotweed very close to coming into our garden

[afkonholidaynearleek]

Hi all, long time MN user but first time posting in Gardening :)

My neighbour has had Japanese knotweed in their garden for the past couple of years. They are aware and are treating it - not nearly as much as I'd like to see - but late last summer one stem appeared about four feet from the border between our properties. I am aware it is against the law to let it spread into neighbouring properties, but I really don't want to have to go down that route. I get on with my neighbours but we're not that close.

I am very anxious it will spread into our garden from this spring. We are also looking to sell our house in the next couple of years, which is a real pain in the ass as we'd have to disclose it.

Between our gardens we have a lot of shrubs and various trees, but it is sparse in places and there is nothing that provides very heavy shade to prevent knotweed growth into our garden. I'd like to have a raised planter alongside our boundaries with lots of shrubs and flowers, or even trees.

Do you have any recommendations for plants I could put in the soil in the next month that might deter Japanese knotweed from spreading into our garden?

Have you considered membrane:
https://www.hy-tex.co.uk/product/root-barrier-c3/?gclid=EAIaIQobChMIss2PuouKhAMVc5ZQBh2mEAO4EAAYAyAAEgLbbfD_BwE

Do you have it on authority that heavy shade makes any difference?

@WhatWouldJeevesDo Thanks for the link. I've thought about using a membrane but there are a lot of tree roots in the area (willow, apple, pear, cherry, elder etc).

I've noticed that with the main clumps the weeds, they haven't grown in the shadow of a very dense tree at the end of the neighbour's garden. They also haven't spread past some very thick tree-like shrubs in the neighbour's garden on the other side. We have no such natural barrier, sadly. I'll have an exploratory dig again, I think, to see if a membrane is a viable option.

Bamboo was the first thing to come to mind as it’s fast growing. Not all types are invasive. It may be a bit early to plant it now.
Instant heavy shade sounds expensive to create.

Are they having it treated professionally? We have knotweed on our farm, and it's just a case of getting the professionals in. I know you shouldn't have to, but so ensure a smooth sale it might be worth asking if you can pay for a professional?

It does go if treated properly so I’d pay for someone to treat theirs if possible. Would be cheaper in the long run!

They are getting theirs treated professionally, but I feel like it's not enough to stop the spread. I didn't feel so bad about it until that shoot that came up 4ft from the boundary. I know it takes a few years to eradicate it but this coming spring is really stressing me out. I first noticed it in July 2022, so we're coming up to two years in now.

I am dreading mid-March when the first new shoots tend to appear. God, it's such an annoying weed!

Buy some glyphosate weed killer, it's really not a big deal if you keep on top of it:

Amazon.co.uk : glyphosate weedkiller

When I bought my house I had a lot of knotweed in the garden and sprayed with glyphosate every time I saw it, I haven't seen any stems for a few years.

Getting JK out of bamboo would be a nightmare

I would consider moving now as if it comes into your garden, you might have a problem selling.
I overreact to things though so feel free to ignore that idea!

The only issue with bamboo as a pp mentioned is that's also invasive - it would put me off as a buyer.

They are getting theirs treated professionally, but I feel like it's not enough to stop the spread.
Perhaps they don't realise? I can imagine someone thinking, "I've paid a professional to sort this; I'll trust them & their methods and I can stop worrying about it now". Maybe you need a conversation with the neighbours to ask if the professionals are on top of their brief,. You never know, they might be booked in for next week.

We bought a house with a history of knotweed in the garden. I'm sorry to say that what I have to tell you probably isn't going to make your day. it was great for us as buyers but not for the sellers.

firstly its difficult to get a mortgage on a property with knotweed and there were only a couple of lenders that were prepared to offer us a mortgage even though we had a great deposit and excellent credit history. It meant we couldn't access really good interest rates. They also required a lower loan to value because of it and we had to find an additional £30k

there had a be a proper insurance and treatment plan in place and we had to submit all the paperwork and an additional assessment from the person who treated it. The lenders also required that there had been no signs of growth for 2 years. We were very lucky that the treatment plan had been in place for 5 years.

these above conditions worked in our favour as the property had been on the market for ages as several sales had fallen through due to mortgaging issues. We ended up getting around £30k off the value of the house basically because of the knotweed.

because of the above I would ensure you do everything in your power to prevent the knotweed coming on your property as you may end up with a property that is unsaleable for several years unless to a cash buyer. I don't want to panic you but you need to be all over it like a rash if you want to move in the next 5 years.

fortinately we have seen no signs since we moved in in 2017 however if we do any building work in the future we will have to pay for professional disposal of the soil if we want to take it out of our boundary

good luck x

Plus I'm pretty sure but not certain that you only have a legal obligation to disclose knotweed if it's appeared on your property not the neighbours so selling asap might also be an option

Go and speak to the neighbour, say you're concerned, offer to contribute to the cost of more aggressive treatment.

Oh and FYI if the treatment is done by a professional it's only twice a year I believe in autumn and spring. By the time we moved in it was down to the final treatment and just checking visits every year which have now ended

Thanks for your insight, @StiffyByngsDogBartholomew. I forget that time has to elapse between treatments, which is what has made me feel like not enough has been done about it. In reality, it has been dealt with for two years so far in their garden (summer 2022 was when I told them about it). I just hope the same can be said in the other neighbour's garden, I have no idea if they've been treating it or not.

The lenders also required that there had been no signs of growth for 2 years. We were very lucky that the treatment plan had been in place for 5 years.
I definitely hadn't realised this 🤔With any luck we'd have no more growth after three years, which sort of coincides with our ideal time to move.

With any luck, it'll stay on their side of the boundary.