Lycoris squamigera, L. longituba, L. chinensis and L. sprengeri are all perfectly hardy for me. I have never tried L. radiata, but I have always read it was hardy to zone 7 anyway? The problem with it in my zone is that it produces foliage in autumn which can then be damaged or killed by the multiple freeze-thaw cycles of winter and early spring, and this is said to weaken and eventually kill the bulb. However, in areas that consistently have good, deep, reliable snow cover that protects the foliage, I imagine L. radiata could survive and thrive in much colder zones. Good luck with your experiments!

In Oklahoma I had chinensis, radiata, sprengeri, aurea, all successfully. This year with the alternate freeze thaw that the poster above mentioned (and being in the deep freeze for long periods), I lost the radiata foliage in mid to late December.

Plant Delights sells a L. aurea from Guizhou, China that they claim is hardy in zone 7. The commercial form commonly available from big bulb vendors is not. The bulb will survive, but the foliage is destroyed by temperatures in the mid 20s. Consequently, the bulb gets smaller and weaker each year and never flowers.

This winter, our low was 6 F. The foliage survived on all of my L. radiata. Some plants looked pretty bad afterwards, but others had spotless foliage. Presumably, there is some variability in the hardiness of different clones