It would be good if someone who grows Doubloons in Minnesota or another USDA Zone 4 area would check in re. the hardiness of Doubloons. I have some doubt that it would handle “normal” Zone 4 winters without some protection. Mature canes did fine in St. Louis, but Doubloons grows so vigorously that it usually has a lot of new growth at the end of the year and loses these canes over the winter. It might not have this late-season growth in Zone 4, but I’m not sure that even the mature canes would handle “normal” Zone 4 winters.
Over the 30 years that I have had Doubloons here in KS it has always frozen back at 0 F or lower and generally done OK at +10 F. I cover it deeply, a foot or more of leaves but anything higher freezes, even if it was produced very early in the season. So I have had blossoms may half those years. I have not noticed that the newer wood is particularly more susceptible than the older. The warming trend of the past decade has definitely worked in its favor, so I woudl say it is right at its limit. AS I mentioned some time earlier, in Wichita it does hold up. They are a zone south of us.