Allium not flowering

marisa.shek

I planted an allium (Globemaster I think) as a plant, two years ago when it was in full bloom, then in the first winter the leaves died back but it came back and bloomed again in Spring/Summer.

 

This last winter, the leaves remained green, did not die back and I did not cut them back. This spring I have no flowers and there does not appear to be any buds coming through for Summer either. While the leaves look unbelievably gloriously green, thick and healthy, did I make a mistake in not cutting them back for winter?