Hello Maryl
I planted the Allium afflatunense both as the plain species and as cultivar Purple Sensation. I put them in a border with tall perennials, light sandy soil and irrigation in Berlin. I tended the garden in the two following years. Only thing I noticed was the Allium groups getting slightly bigger and when I transplanted a couple after flowering it looked like they formed few brood bulbs. I let the flower stalks stand for a while as they looked beautiful and cut them back only when they tipped over. And I never found any onion- or Allium- like seedlings when weeding.

cheers, Linaria

thanks Lin. I guess they shouldn't be invasive then. I hope not because they are planted now.