I was interested in the same question.

What type alliums do you have?

I can't tell you what variety I have as they came from a friend, (haven't found a picture exactly the same yet.) They self seeded all over her garden and were threatening to take it over. We get cold long winters here so a bit of cold might help the seeds, and judging by the size of plants I have this year, I would expect it to take about 3-5 years to flower. At 2 or 3 years of age the bulb is about double the size of a bluebell bulb. Good luck and I hope this helps.