i think just wate a bit longer some plants take a while to mature and as flowers are to do with breeding and being mature its more than likley just a matter of time .i mite be wrong ofcourse lol

I bought several different variates from a garden centre about 3 years ago flowered first year and haven't again since.
Mind you i do leave them in the ground all winter and they come up every year hopefully this year they'll flower...