Troubleshooting
Welsh Onion problems — and how to fix them
Welsh Onion (Allium fistulosum) 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 downy mildew
Pale, fuzzy grey-violet growth on leaves in cool damp weather; improve spacing and airflow, avoid overhead watering.
Thrips damage
Silvery streaking and stippling on leaves from rasping thrips, worse in hot dry spells; rinse foliage and encourage predatory insects.
Bolting in heat or stress
Plants throw up round flower heads and leaves toughen; cut flower stalks early and keep soil moisture steady to delay it.
Crown rot from wet soil
Yellowing, collapsing clumps in waterlogged ground; plant in free-draining soil or raised beds and avoid winter sogginess.
Prevent welsh onion problems before they start
Most welsh onion issues are care-mismatch, not bad luck. Dial in the basics:
Looking for welsh onion in general rather than its problems? Read the full welsh onion care guide — light, water, soil and feeding.
Welsh Onion problems — FAQ
Why is my welsh onion onion downy mildew?
Pale, fuzzy grey-violet growth on leaves in cool damp weather; improve spacing and airflow, avoid overhead watering.
Why is my welsh onion thrips damage?
Silvery streaking and stippling on leaves from rasping thrips, worse in hot dry spells; rinse foliage and encourage predatory insects.
Why is my welsh onion bolting in heat or stress?
Plants throw up round flower heads and leaves toughen; cut flower stalks early and keep soil moisture steady to delay it.
Why is my welsh onion crown rot from wet soil?
Yellowing, collapsing clumps in waterlogged ground; plant in free-draining soil or raised beds and avoid winter sogginess.