Onion gone to seed

Break the flower heads off!!!

The bulbs will still grow but will have thicker necks having thrown up a flower head and will not keep for very long.

Various kinds of stress to the plant will make it decide that it's time to reproduce itself; unfortunately this can be excessive cold followed by heat, or drought (say no more!)

Some varieties are more prone to bolting than others; some sets are heat-treated to try and reduce this tendency but it's not foolproof.

I concentrate on shallots these days, because although they can also bolt they don't seem to do so as much as onions, and are also much more expensive to buy in the shops.