MaryL, sorry you haven't had a response yet.

I put purple sensation in the ground this weekend, and I'm at the border of zones 7 and 6. I'd say I've planted them about four times over the years, and have never had a problem with them taking over.

AFter I posted that question I looked at my notes from years ago when I had planted some different varieties of Alliums and I planted them in the fall about now just as you said. I DO appreciate you helping me though. I know I don't have anything exotic because I got the bulbs from Ace Hardware, so couldn't understand the lack of response here. I really thank you for easing my mind however about them being invasive. I was concerned about that a lot.
Maryl

If you're worried about them reseeding, just clip the flower stem off at the base and discard. The flowers will get smaller the following year if allowed to go to seed, and eventually stop blooming, anyway. Deadheading will keep them strong longer.

I knew not to let any bulb in the Allium family spread seed, but its good advice to be reminded of again. No, it's those darned tiny (smaller then a pea in some cases) bulblets that form all around the main bulb that spread faster then the Asian Flu. I like the Drumstick Allium, but had I known it would spread like it does I might have been more careful about where I planted it. As it is, I'm glad to hear that Purple Sensation does not have those tendencies. To be on the safe side I'm going to plant the bulbs in a buried pot I have in my border.