Only reason that seems likely was the weather, but if you're having the problem with just one cultivar, hmm, unless that one is just more sensitive. I have an old fashioned purple/brownish one that blossomed normal but it is on the south side of the house, right next to the steps and even a geranium survived this winter so I'm thinking it's a micro climate area. That would still be reasonable to think it's the weather here.
So sorry I can't be of more help...
