Troubleshooting
Onions problems — and how to fix them
Onions (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.
Bolting to flower
Cold spell after planting triggers premature flowering; use heat-treated sets.
Small bulbs
Wrong day-length variety, planted too late, or under-watered during bulb formation.
Soft rot at the neck
Wet conditions at harvest; dry bulbs thoroughly before storage.
Downy mildew
Wet leaves and humid air; rotate planting site and improve drainage.
Onion thrips
Silvery streaks on leaves; tolerable in small numbers, treat with horticultural soap if heavy.
Prevent onions problems before they start
Most onions issues are care-mismatch, not bad luck. Dial in the basics:
Onions problems — FAQ
Why is my onions bolting to flower?
Cold spell after planting triggers premature flowering; use heat-treated sets.
Why is my onions small bulbs?
Wrong day-length variety, planted too late, or under-watered during bulb formation.
Why is my onions soft rot at the neck?
Wet conditions at harvest; dry bulbs thoroughly before storage.
Why is my onions downy mildew?
Wet leaves and humid air; rotate planting site and improve drainage.
Why is my onions onion thrips?
Silvery streaks on leaves; tolerable in small numbers, treat with horticultural soap if heavy.