This is the exact info I was looking for also. Do you have your persicaria in full sun or part shade. I am a zone 5 and mine is in full sun but I think it gets too hot and too much sun so am considering moving it to partial shade although I don't have much partial shade. I have never been impressed with my Persicaria but loved it when I saw it in David's pictures.

I don't know if you are intersted in this kind or not, but I grow Persicaria affinis (sometimes called affine I think) 'Himalayan Border Jewel'. I have seen this cultivar called just 'Border Jewel' and the common name Himalayan Knotweed. This is a groundcover kind of knotweed, though it has never gone beyond a small-ish mat for me. Seems to spread more in areas that do not have hard-packed soil (for me that means sandy spots in my garden). I have had it for about five years. It has only bloomed ONCE, and that was when I bought it, lol! It does get some sun, but maybe not enough. Maybe I need to give it a stern talking to. Hey, it worked with the Phlomis...;-) -Mindy, how invasive do you find the P. bistorta superba/suberbum? I love the look of it, but have avoided it because of the horror storries. Hope you will let us know if you write that article (on your blog??) on them. CMK

what your base soil ... drainage wise? and is the standing spring water.. related to snow thaw??? .. prior to ground thaw??? in livonia... i had a spot that was under water for a week or so.. at thaw.. when everything was dormant... and as soon as the ground thawed ... it was all gone .... i dont recall anything failing due to such ... same area .. after a good storm.. might do the same for a couple hours ... no effect other than to completely wet the soil in summer.. when it was needed ... in that garden.. i had high organic MI peat type soil ... well draining ... i did not grow the particular plant you are asking about .. but i did grow knotweed.. LOL .... i did have painters palette, but i dont recall if it was in the wet spot ... ken

The bed where the persicaria is looks a lot worse now... this pic is at least 5 or 6 years old. I am not interested in rejuvenating a mixed perennial flower bed. I appreciate those who have them, but they are not for us. I want to simplify it - prefer groupings - maybe 3 or 4 varieties of plants/shrubs at most. They planted over 10. It was a hodgepodge mess by the time we moved into the place in the spring of 2015