Why Are My Onions Small? Causes and Fixes
Why onion bulbs stay small: wrong day-length type, late planting, crowding, weeds, low nitrogen early, drought, too much nitrogen late, and bolting.
Muhammet Elma
3 November 2026
2 min read
Bulb size is mostly decided by how many healthy leaves the plant has when bulbing starts; each leaf corresponds to a ring of the bulb. Anything that limits leafy growth before then gives small onions: the wrong day-length type, late planting, crowding or weeds.
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Common Causes
- Wrong type for your latitude: short-day onions in the north bulb before the plant is big.
- Late planting: too little time to grow leaves.
- Crowding and weeds: onions have thin leaves and compete poorly.
- Low nitrogen early in the season.
- Drought during bulb swelling.
- Too much nitrogen late: thick necks and poor bulbs.
- Bolting.
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How to Grow Bigger Onions
- Choose the right day-length type.
- Plant on time and space 10–15 cm apart.
- Weed regularly.
- Feed nitrogen early; switch off as bulbs swell.
- Water about 2.5 cm (1 in) a week.
More Onion Guides
- How to Grow Onions: The Complete Guide
- Onion fertilizer
- Onion pests and diseases
- When to plant onions
Frequently Asked Questions
Why are my onions not bulbing?
Usually the wrong day-length type for your area or too much late nitrogen.
Does cutting onion tops make bigger bulbs?
No. The leaves feed the bulb; removing them makes bulbs smaller.
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Muhammet Elma
TarlaTapan guides focus on practical, field-tested growing advice. Corrections and suggestions are welcome at info@tarlatapan.tr.