The only information that I could find about when to pull an onion stated that you pull it when it falls over at the neck. So I went out and pulled every onion that had fallen at the neck. Those onions looked a lot like the 1st onion in the picture.
At this point I wondered if I had planted the onions too late. Couldn't have? All the nurseries were selling the onion plants so they would know right (in Jan for North Texas)?
I finally found something that said to wait about two weeks after they had fallen at the neck. So I did that with the next set and they looked like the middle onion.
Ok. Now we are looking more like an onion; though still small.
I now acknowledge that several sites did say that you should wait until the tops had died or the onions popped above the soil. However, all of my tops were still green when they fell over. So I decided that for the last few that were out there, I would just wait...until. Until what? I didn't know, but there were only a few and I was just going to see what happened.
Well, I waited and waited and finally the tops of these onions started popping above the soil. And they were whoppers. The tops had fallen at the neck at least 3-4 weeks ago. The tops were still green. I keep waiting. It finally became clear that they were no longer growing, so I pulled them and out came the last onion (in the picture). A whopping 4" across (forgive the camera angle, but it is 4" across).
So when to pull an onion?
Well, first be sure not to bury it too deep when you are planting so that it will bulb. Then, don't pull them until you can see them. If they haven't popped out from under the soil, then leave them alone (or take a peak / pull one just to see). Even after you can see them, just watch them for a while...you'll know when they are done. Just make sure they have fallen over at the necks and the neck is soft and dry. The stem may still be green; mine never did die off.
The rest of our onions are still curing, but I'll share the harvest once they are done.