Troubleshooting
Spring Onion problems — and how to fix them
Spring Onion (Allium fistulosum 'White Lisbon') 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.
Downy mildew
Pale patches with greyish mould on the leaves in cool wet weather. Improve spacing and airflow, water at the base, and rotate alliums around the plot.
Onion fly
White maggots burrow into the base, causing wilting and collapse of young plants. Use insect-proof mesh and avoid leaving thinnings lying around, which attract the flies.
Slow germination in cold soil
Seed sown into cold wet ground rots or germinates patchily. Wait for soil to warm, or sow in modules and transplant in clumps.
Bolting
Overwintered or stressed plants run to flower in spring, toughening the shank. Sow appropriate winter-hardy strains for overwintering and harvest before flowering.
Prevent spring onion problems before they start
Most spring onion issues are care-mismatch, not bad luck. Dial in the basics:
Looking for spring onion in general rather than its problems? Read the full spring onion care guide — light, water, soil and feeding.
Spring Onion problems — FAQ
Why is my spring onion downy mildew?
Pale patches with greyish mould on the leaves in cool wet weather. Improve spacing and airflow, water at the base, and rotate alliums around the plot.
Why is my spring onion onion fly?
White maggots burrow into the base, causing wilting and collapse of young plants. Use insect-proof mesh and avoid leaving thinnings lying around, which attract the flies.
Why is my spring onion slow germination in cold soil?
Seed sown into cold wet ground rots or germinates patchily. Wait for soil to warm, or sow in modules and transplant in clumps.
Why is my spring onion bolting?
Overwintered or stressed plants run to flower in spring, toughening the shank. Sow appropriate winter-hardy strains for overwintering and harvest before flowering.