Japanese knotweed- overhyped?

patman99

They were talking about Japanese Knotweed on BBC Essex's 'Ken Crowther' gardening show a week or two back. The presenter and his guest advised that the best way to get rid was to use a glysophate based weedkiller and to spray weekly.
They said it can take up to 3 years to kill it off completely and that whilst it was safe to compost the leaves, the roots needed to be dried-out fully before disposal in order to prevent re-growth.

Apparrently it is no longer a notifiable plant and you can actually plant and grow it. The chap who first brought it in to the UK many years ago, planted a small patch in the middle of a lawn and it still grows in a controlled manner today.

As a plant, it is very robust and can break through concrete and tarmac. It is certainly not something I'd like to have to deal with.

jennifernil

We had a patch of it, about 15 sq m, appear in the grounds of our guide hall, probably due to someone fly tipping garden waste.

We had it treated by a local specialist firm over 3 seasons, the cost was around £2500 and we have a 10 year insurance backed warranty, with annual inspections.

It didn't threaten the building, but a few stems did push up through the adjacent pavement.

moneyistooshorttomention

MrsFingersCrossed wrote: »

I just wrote a long reply but internet cut out so lost it. I was basically saying have a look here: http://www.environetuk.com/


(Mark Thompson was helpful when we were looking at a house with Knotweed just over the boundary) We did a lot of research and discovered it can be a problem to get a mortgage but apparently not if it has been professionally removed and there is a maintenance plan in place. Hope this helps.

Someone was saying on a thread on the gardening sub-forum the other day that, even after a professional management plan has been done that its not deemed to be possible to start digging around in the soil and using it as per normal afterwards - ie the JK is out of sight and stops growing, but still disrupts things afterwards to that extent.

I don't know if that is true or no? Can anyone confirm? I always thought that once that "professional" treatment had been done that it was back to status quo afterwards and treat the garden/ground exactly as you would have if the JK had never been there in the first place iyswim and you could dig around all you please?

moneyistooshorttomention

MrsFingersCrossed wrote: »

Funny you say that, Oystercatcher. Yesterday to my horror I discovered a tiny new suspicious 'weed' poking through the gravel by our doorstep. We've lived here for nigh on 30 years and that is the first time I've ever seen anything like it. It's in the incinerator now.

I couldn't have recognised it before I moved. I can now spot it a mile off and the two things I recall as best identifiers are that, when its just started growing the shoots look like red-flushed asparagus stems growing in the ground. Also, when the leaves are young they are quite arrow-shaped and the leaf edges sort of "furl inwards". The leaves then go more opened-out and wide with a little pointy "tip" at the top edge when mature.

That's how I tell myself how to identify it.

The thing I'm not quite sure of is on its method of spreading. I know it spreads from the roots - but a couple of days ago I was reading comments about the flowers being seeds (whereas I've always read it cant seed itself - at least in Britain). That author also seemed to think it could spread itself via portions of stem as well (I'd be glad on clarification of that myself - as I'm aware of a house-owner in walking distance from my place having it in their garden and not treating it properly - despite knowing what it is).

MrsFingersCrossed

Can of worms! I've read it doesn't spread by seed too but it seems too much of a coincidence that we'd viewed a house where it's in the vicinity (with a maintenance plan in place) and just weeks later new shoots appeared on our doorstep. We'd recently filled in the property questions form (for our buyer) saying none on the premises or in the vicinity, so horrified to discover said suspicious weed in gravel. We're reassuring ourselves the statement is still true because we pulled up tiny shoots and incinerated them, hence no JK on premises, still. But a shock nonetheless.

Zekko

moneyistooshorttomention wrote: »

The thing I'm not quite sure of is on its method of spreading. I know it spreads from the roots - but a couple of days ago I was reading comments about the flowers being seeds (whereas I've always read it cant seed itself - at least in Britain). That author also seemed to think it could spread itself via portions of stem as well (I'd be glad on clarification of that myself - as I'm aware of a house-owner in walking distance from my place having it in their garden and not treating it properly - despite knowing what it is).

From some online sources:

Japanese Knotweed can produce seeds, but it is rare for these seeds to germinate. The most common method of dispersal is by means of stem, crown and rhizome.

New plants grow from the nodes of pieces of green stem in soil or water. Mechanical cutters, such as flails will spread knotweed in this way. If stems are dried until they are dark brown they will not regrow unless the crown (base of the stem) is still attached.

The crown can survive drying and composting and will quickly produce new canes. If you dispose of knotweed canes by drying or composting, it is important that the stems are cut above the crown, rather than pulling the plant, which will dislodge the crown.

Rhizomes are not roots, they are underground stems and can reach a depth of 3 metres (10ft) and extend up to 7 metres (23ft) away from the parent plant. It only takes a 1cm section of rhizome or crown to propagate another plant. There is a leaf join or ‘node’ (growth point) roughly every 3cm on the rhizome (33 per metre). When treated some of the growth points respond by producing a new shoot. (underground stem section).

Rambosmum

We had it, the previous owners had cheekily cut it down and though it had started to grow, neither the banks surveyor nor our surveyor noticed it and so getting a mortgage was no issue! 2 years later we worked out what the weird plant in the front garden was and £500 later it was gone and we've had no issues since.

moneyistooshorttomention

Zekko wrote: »

From some online sources:

Japanese Knotweed can produce seeds, but it is rare for these seeds to germinate. The most common method of dispersal is by means of stem, crown and rhizome.

New plants grow from the nodes of pieces of green stem in soil or water. Mechanical cutters, such as flails will spread knotweed in this way. If stems are dried until they are dark brown they will not regrow unless the crown (base of the stem) is still attached.

The crown can survive drying and composting and will quickly produce new canes. If you dispose of knotweed canes by drying or composting, it is important that the stems are cut above the crown, rather than pulling the plant, which will dislodge the crown.

Rhizomes are not roots, they are underground stems and can reach a depth of 3 metres (10ft) and extend up to 7 metres (23ft) away from the parent plant. It only takes a 1cm section of rhizome or crown to propagate another plant. There is a leaf join or ‘node’ (growth point) roughly every 3cm on the rhizome (33 per metre). When treated some of the growth points respond by producing a new shoot. (underground stem section).

Thanks for that.

1. Can I have chapter and verse of where you found that please? - as one of my concerns about the nearby JK is that the Council come around strimming in that area at intervals and don't seem to believe me when I tell them they need to get onto that antisocial home-owner to remove it and NOT strim anywhere near it until they've successfully dealt with that home-owner.

2. I'm not quite sure what bit is meant by the "crown". Which bit is that please?

moneyistooshorttomention

Rambosmum wrote: »

We had it, the previous owners had cheekily cut it down and though it had started to grow, neither the banks surveyor nor our surveyor noticed it and so getting a mortgage was no issue! 2 years later we worked out what the weird plant in the front garden was and £500 later it was gone and we've had no issues since.

Very naughty of that previous owner to try hiding it like that! Did you try and claim that £500 (plus compensation for the worry of it) back from them or anything?

(That reminds me - I've not made that suggestion to a couple of friends of mine here that recently bought houses, only to find the previous owner had carefully not mentioned they had JK in the garden....note to self to do so....).

Gingernutty

moneyistooshorttomention wrote: »

I'm not quite sure what bit is meant by the "crown". Which bit is that please?

This is a crown.

http://www.japaneseknotweed.org/images/waht_invasive.jpg

A large node where a number of stems have grown.

Underneath, is what will look like the stump of a small tree.

http://www.knotweed-removal.co.uk/graphics/crown.jpg

Two very useful sites

http://www.knotweed-removal.co.uk/welcome-to-the-knotweed-company.php

http://www.japaneseknotweed.org/index.php?page=what#