Zone 4 hardy!
I’m April 2020 I had 3 plants mailed to me. They arrived in wonderful condition! Way bigger and stronger than I expected. I kept them in small pots ever since. Thru neglect , 2 died, but the remaining one survived being outside in the MN minnesota winter 2023 in Saint Paul. There was a lot of snowfall to insulate the roots, but the top was fully exposed and there was no die back in a very exposed spot. I will plant into the lake bottom this year and see if it survives the ice formation and potential ice shifting this winter. I can’t find evidence, but I think the UMN Arboretum once had a patch of cork wood in Chanhassen. My motivation for planting is because Bald cypress hasn’t been hardy for me and Buttonbush is the only other woody plant hardy here that can survive perpetual standing water to that depth. Boat made waves are otherwise eroding shorelines and I want to stop that. Blue flag iris, burreed, hard and soft bulrush are all pretty successful erosion control, without going for the dominant cattail or reed canary grasses, both of which are thought to often be hybrids of native and non-native.