I want to share with you my observations on I. uniflorum winter survival.
Last winter we had 2 weeks long period of sever frost down to -25 C (might be -30 at the ground level) without any snow cover. The soil was deeply frozen, possibly as deep as 50-70 cm.
Ipheion autumn leaves died, but otherwise the plants started healthy vegetation after thaw. No visible bulb loss. Effect on blooming I will see in June.
Some white Ipheions ("Alberto Castillo"??) planted late autumn do not show any vegetation, yet (may be too early).
My main observation is the extreme frost hardiness of Ipeion. It is better comparing to many other bulbs regerded as hardy. This winter I lost many Crocuses, specially from chrysanthus/biflorus group, Crocus speciosus, even many crocus tommasinianus. Hyacynthoides hispanica partial loss, Galanthus elwesii - the same.
I still wonder how this plant obtained this feature growing wild in the very mild climate of Uruguay.
Jacek, Poland, Central Europe, winter zone 6A