I live in North Carolina, USDA Zone 7b---not really "Southern", but not "Northern" either. The problem with dormants here is: dormants are very resistant to freeze damage while in the dormant state. However, once growth gets going, the new leaves are less and less able to tolerate freezing. A few years ago we had an unusually warm spell in March/April that lasted for a couple weeks. Then, we had a week where the low temps were in the low twenties down to teens. The Dormants suffered as much as the Evergreens.
I think the problem with trying to grow dormant daylilies further south is the problem of varying temps between daytime highs that start growth--and nighttime lows that repeatedly damage the plant until it gives up. Evergreens seem to bounce back quickly from mild freezes--but if they freeze to the ground--they are pretty much done for. Some Evr's have more antifreeze and can stand the extremes of cold---but they are rare. Every winter I lose at least a half dozen plants. 4 out of 5 are EVR unless there are no lows below 17 degrees. Then it is an even split between Evr's and Dor's.
