Troubleshooting
Ailsa Craig Onion problems — and how to fix them
Ailsa Craig Onion (Allium cepa) 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.
Onion white rot
Sclerotinia cepivorum causes fluffy white fungal growth at the bulb base. No chemical cure; remove and destroy affected plants; do not grow alliums in the same bed for 8+ years.
Onion fly
Larvae tunnel into bulbs, causing wilting and rotting. Cover with fine insect mesh from sowing to midsummer.
Downy mildew
Peronospora destructor causes grey-purple fuzz on leaves in wet weather. Improve air circulation; avoid overhead watering.
Bolting
Premature seed-head formation, especially after a cold period followed by warmth. Remove seed heads promptly; use bolt-resistant sets or sow at the correct time.
Neck rot (Botrytis allii)
Soft rot at the neck during storage. Ensure bulbs are fully cured in the sun before storing; store in a cool, dry, airy place.
Prevent ailsa craig onion problems before they start
Most ailsa craig onion issues are care-mismatch, not bad luck. Dial in the basics:
Ailsa Craig Onion problems — FAQ
Why is my ailsa craig onion onion white rot?
Sclerotinia cepivorum causes fluffy white fungal growth at the bulb base. No chemical cure; remove and destroy affected plants; do not grow alliums in the same bed for 8+ years.
Why is my ailsa craig onion onion fly?
Larvae tunnel into bulbs, causing wilting and rotting. Cover with fine insect mesh from sowing to midsummer.
Why is my ailsa craig onion downy mildew?
Peronospora destructor causes grey-purple fuzz on leaves in wet weather. Improve air circulation; avoid overhead watering.
Why is my ailsa craig onion bolting?
Premature seed-head formation, especially after a cold period followed by warmth. Remove seed heads promptly; use bolt-resistant sets or sow at the correct time.
Why is my ailsa craig onion neck rot (botrytis allii)?
Soft rot at the neck during storage. Ensure bulbs are fully cured in the sun before storing; store in a cool, dry, airy place.