Hi!
I have the same problem. I just recognized it as a problem this year...and now the patch of knotweed is getting out of control. In my research it looks like it's ok to eat when it's about 4-6 inches high, after that it's too tough. In my
experience, after it gets to be 2 feet or taller, it's too tough,
. The best recommendation I found takes awhile, it is to smother it with heavy tarps. To do this you need to get the old sharp stalks out or they'll pierce your tarp. The website that talked about this, said it would take a couple years, and to go ahead and put a
raised bed garden right on top of the tarp. My patch is in a difficult spot to tarp, so I'm tarping as well as mowing it off multiple times, and mowing it really well. Because as you probably already know it can sprout from quite a small piece if it doesn't dry out quick
enough. There was a cool recipe for knotweed fruit leather...and even cooler a recipe for making the taller knotweed into paper. Yep, Knotweed paper, and it looked pretty easy. So it is a multi-useful 'weed'. Lots of things contain oxalic acid. The stems of the rhubarb,
wood sorrel, yellow dock....it's the concentration of it that matters. All these things in moderation and you'll be fine, and your tongue can even be your guide. Who really wants to eat more than 2 stems of rhubarb a day? Or even that many?
Aya