Troubleshooting
White Onion problems — and how to fix them
White Onion (Allium cepa 'Sturon') is generally forgiving once you match its basics, but a few issues come up again and again. Here is what each one looks like, why it happens, and the fix.
Bolting
Cold stress on sets or early planting makes onions flower instead of bulbing, giving a thick neck and poor keepers. Use heat-treated sets like 'Sturon' and plant at the right time.
Onion white rot
Soil fungus that rots the roots and base with fluffy white mould; plants yellow and topple. There is no cure, so rotate alliums on a long cycle and use clean ground.
Downy mildew and neck rot
Wet conditions cause leaf mildew and soft rotting at the neck that spoils stored bulbs. Space well, water at the base, and cure bulbs thoroughly before storing.
Onion fly
Maggots tunnel into the bulb base, wilting and killing plants. Protect with insect-proof mesh and practise good plot hygiene to break the cycle.
Prevent white onion problems before they start
Most white onion issues are care-mismatch, not bad luck. Dial in the basics:
Looking for white onion in general rather than its problems? Read the full white onion care guide — light, water, soil and feeding.
White Onion problems — FAQ
Why is my white onion bolting?
Cold stress on sets or early planting makes onions flower instead of bulbing, giving a thick neck and poor keepers. Use heat-treated sets like 'Sturon' and plant at the right time.
Why is my white onion onion white rot?
Soil fungus that rots the roots and base with fluffy white mould; plants yellow and topple. There is no cure, so rotate alliums on a long cycle and use clean ground.
Why is my white onion downy mildew and neck rot?
Wet conditions cause leaf mildew and soft rotting at the neck that spoils stored bulbs. Space well, water at the base, and cure bulbs thoroughly before storing.
Why is my white onion onion fly?
Maggots tunnel into the bulb base, wilting and killing plants. Protect with insect-proof mesh and practise good plot hygiene to break the cycle.