Cultivating onion is beating me

what's actually going wrong - no bulbs, rotting, bolting? Usual culprits are planting too deep (sets want the tip just showing), not enough sun, or weeds. Onions have tiny roots and get smothered by competition fast. Also worth checking you've got the right type for your latitude, short-day vs long-day. The wrong one gives you lots of leaf and no bulb.