Last year, I decided to let some of my onions go to seed in the front garden so I would have some clean seed for growing sprouts for wintertime salads. This is a trade-off - if you let your onions put up seeds, they won't make big bulbs, so you're giving up that year's production. Of course, I planted my main crop in the regular veggie garden, so all was not lost.
They sent up lovely white puffball flowers, and I was hopeful for a good seed harvest.
Unfortunately, I didn't plan on an adorable three-year-old boy deciding it was fun to grab them by the stem (which were just his height!) and pick all of those lovely flowers.
So I gave up on those, since the bulbs were too small to eat.
Fast forward six months to this spring, and what do I find in my front garden bed but thick, healthy onion leaves coming up where those decapitated onion flowers stood last fall?
(the leaves are brown at the tips from an earlier frost)
So, the moral of the story appears to be that onions overwinter just fine, even way up here. Which leads to my new plan - start next year's onions from seed this year, leave them in the ground over winter, and let them grow to full size the following year (basically growing my own sets instead of buying them). I think I'll try again (in a different bed) to raise some seed (hopefully four year olds have more self-control than they did at age three!)