I planted 5-6 giant allium bulbs a few falls ago (this is their third summer). Only 3 of the flowers are blooming, and they are all smaller than previously. The others are just producing sad looking foliage. I've heard these guys are short lived, but just 2 summers?

I'm in zone 5 and while they don't get a ton of water, they should be fine.

Should I try to divide them in the fall? How do you tell if they can be divided?