I used the bottom of some onions that I had and put them in water to root. Once I did that, I planted them and they are growing very nicely. They now have flowers at the tops and I'm assuming that is where the next seeds come from. I don't know how to get the seeds and/or when. Any help? I'd really appreciate it.
Growing Onions From Onions
Certified GKH Gardening Expert
Your onions have "bolted" (grown flower stems), which means they need to be pulled out of the ground and used as soon as possible.
Onion bulbs "bolt" when the plant is under stress.
This article will explain some probably causes for bolting, what to do with the plants right now, and how to keep this from happening again:
Here is an article on seed collection.