Pinch them if you want to maximize bulb growth. Though once they have bolted the bulb will not get much larger. If they are planted pretty close I would pull the bolters and eat them to give more space to the others.

The same thing is happening to a few of my onions. From what I could find by googling it, sounds like it's caused from erratic temperatures (which is almost always the case in Portland, OR this time of year). Also, it's definitely not a good thing, as onions aren't supposed to flower, and you might as well use them now (as PNbrown suggests).

Mine are flowering right now because of the temp fluctuations (I'm in NorCal). The previous renters planted them, so I don't care that they're not being prolific, but they're total duds. I pulled a couple out to see what they looked like, which was giant green onions. Kept them out to dry for a few days and somebody who isn't allergic to them cracked it open, no good at all. I'll just keep them until they finish flowering and have somebody pull them all for me. This was my exact question a week or so ago.

Thanks for the helpful responses, pnbrown, shermthewerm, and allhaileris.

Somewhere in the far reaches of my mind I remember reading someplace long ago that one could double over the onion stalks in the middle and abate this flowering process.

Do you recall this from somewhere?

Sounds interesting, albert_135. :)

I pulled up one of my "bolted" onions, and there was no bulb to speak of.