WE haven't lifted our onions yet as they are still green
Wow, mine started dying back a while a while ago and I lifted three weekends ago. We have v dry sandy soil which I expect affects the growing season length as I don't tend to water v much either. I think one year they died back in June! This year I used enviromesh which protected from pests and helped keep in the moisture. If I hadn't been successful I was going to give up on onions, so pleased I gave it another go. Also added chicken manure pellets at beginning of planting out and May I think. The soil had previously been manured for potatoes.
I should have mentioned, I used the method on this site http://www.gardenstew.com/about11490.html though tucked the onion necks under the same onion rather than the one below, which seemed to work ok. None fallen off so far!