agnesandzoe's picture

Help! hybrid japanese knotweed in my garden?

Observed: 2nd July 2012 By: agnesandzoe
the patch
leaf size
heart shaped leaves
leaf size

Hi everyone,
We believe that the weed we found at the back of our new house may be hybrid Japanese Knotweed.
For more images please see:
Please could you help us ID this weed to make sure we use the most optimal herbicides to eradicate it.
Your help would be very much appreciated.
Cheers, Agnes

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WS159's picture

I can't id this for you but

I can't id this for you but if it is the dreaded Japanese Knotweed then there is some useful information at this link.

agnesandzoe's picture


Thanks, we are aware of these options but the optimal herbicide depends on the species.
Anyone feeling up to IDing this plant?
Cheers, Agnes

BDeed's picture

Can't be certain...

...But I don't think this is a Knotweed, though at a glance this does look very similar, the leaves are not alternating from a stem and the shape of the leaves doesn't look right (even for a hybrid), i wouldn't expect the lobes to overlap and the leaves do seem to be on quite long stalks.

I would expect this is some strange garden plant but can't id it at the moment, shall keep looking.

agnesandzoe's picture


If there's any picture I can take that will make identification better, or any other bit of info about this terrible plant, please don't hesitate to let me know!
We dug up one plant to check what the roots look like (and carefully returned to ground immediately...). The roots are thick knobbly and orange but not very deep.
This is currently a contained patch of about 3*2 meters, we only just moved in so don't know if it was there last year.

BDeed's picture


I referred your picture to a local Ecologist who in turn has sent it to other top botanical experts, the consensus seems to be, we aren't sure but maybe Fallopia sachalinensis... see replies below:

"Regarding the knotweed - it looks like Fallopia sachalinensis to me
(Giant Knotweed), going by the very cordate bases to the leaves - it is
most certainly a relative of F. japonica. These are both the parents of
our Hybrid Knotweed (F x bohemica)!

F. sachalinensis has mega-sized leaves when mature and is quite
astounding when you see it. It needs to be treated with glyphosate
(Round-up) at least three times a year (June, Aug and Oct). Cut first
(June and Aug treatment) to encourage new growth then cover the leaves
with the herbicide. Spray again in Oct when senescence has begun, the
plant will take in the herbicide to the roots at this time. This needs
to be repeated for at least three years, maybe more, but keeping up the
treatment is most important.

Another one to look out for is Himalayan Knotweed (Persicaria wallichii)
which I thought it might be, but this has narrower leaves. I have seen
it once many years ago."

And also..

"Sent the photos to Peter Gateley and Phil Smith to get their view on the
strange plant...Phil agrees it is likely F sachalinensis but Pete isn't
so sure.

Need the flowers to be completely certain! Just thought I'd let you know
their take."

agnesandzoe's picture

thank you!

Thank you very much for your help.
Not great news, but at least we know what we've got and can take action.

We thought it might be the hybrid fallopia x bohemica
but in any case - the key things is it is some variant of knotweed, and the exact variety is probably not so key!

We'll be fighting the good fight for the next few years, then.

cabbageleek's picture

It is most certainly not

It is most certainly not Fallopia sachalinensis, nor F x bohemica, but it could be Persicaria wallichii.

agnesandzoe's picture


Hi cabbageleek,
The leaves aren't as smooth and narrow as those of Persicaria wallichii as far as I can tell, but maybe as there's debate between experts it's better to be safe than sorry.
Thanks everyone!

BDeed's picture

Persicaria weyrichii

Looking at other images myself of this species it does look likely hence my agreement, though i have never encountered it before so i cant be sure.