There is much more information available on the internet; google "knotweed"
and "vinegar weeds".
You wrote, "Black plastic is out as we are organic." Being organic is
commendable, but what does that have to do with laying down black plastic to
suppress weeds? I am unaware that black plastic is not permitted in an
organic garden. That seems to me to be as foolish as saying you can't use
metal tomato cages.
I try to garden organically, but every once in a while, chemicals are
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