After many years of mixed success storing tubers from poor keeping varieties, I can now store them at a rate that is acceptable to keep the variety going but seldom enough to sell them. Two things contribute to success, The first is digging them first before the rain and well before any frost. They need to be totally healthy, strong plants when you dig them and still be growing and blooming well. This goes counter to those frost maniacs that believe a killing frost makes for better tubers, Remember where dahlias grow in the wild it does not frost. And second, cinnamon really works better than anything I have ever used. I "shake and bake" the poor keeping tubers in Ceylon cinnamon. And related to these methods is that you must keep pot tubers of these poor keepers as insurance. And that means two or three not one as the failure rate for their pot tubers is about 25% according to an old expert.