S. rubra ssp is my "pace and wring hands plant". I seem to have many issues with transplanting those. I am learning they do not like a lot of water though. Probably damp not wet with a dousing every so often to flush. I don't know what my problem with those is but one of these days I am going to figure out why I have so many problems transplanting them. They hate me, I swear that's it.
You know Gawd_oOo, there are a few Utrics you could try in that type of an environment too. U. resupinata comes to mind and if you find where to buy one of those, let me know as that's one I'm looking for too. I'd also try U. macrorhiza as well as U. vulgaris.
This is going to sound somewhat outlandish but; if your area tests alkaline, you could raise the pH a tad by using vinegar. A Tblsp into a gallon of rainwater might make what ever CP you ultimately choose feel more at home. Hold at 6.5 and see how the plants you select fair. I know there are people out there who raise pH by using rhodo and azalea products but I'd much prefer to go the route of adding white pine needles and a sprinkle here and there of vinegar in rain water.