Onion Fertilizer: When and How to Feed Onions
How to fertilize onions: soil preparation, nitrogen during leafy growth, when to stop feeding, potassium and sulfur, organic options and avoiding thick necks.
Muhammet Elma
3 November 2026
1 min read
Onions are heavy feeders during their leafy growth stage. Prepare the bed with compost, then side-dress with nitrogen every 2–3 weeks until bulbs begin to swell. Stop feeding nitrogen once bulbing starts; late nitrogen causes thick necks and poor storage.
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Feeding Schedule
| Stage | What to apply |
|---|---|
| Before planting | Compost plus a balanced fertilizer worked into the bed |
| 3–4 weeks after planting | Nitrogen side-dress (e.g. blood meal, ammonium sulfate) |
| Every 2–3 weeks | Light nitrogen until bulbing |
| Bulb swelling | Stop nitrogen; potassium helps bulb quality |
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Tips
- Onions prefer pH 6.0–7.0.
- Sulfur intensifies pungency; most soils have enough.
- Avoid fresh manure.
More Onion Guides
- How to Grow Onions: The Complete Guide
- Onion pests and diseases
- When to plant onions
- Short-day vs long-day onions
Frequently Asked Questions
What is the best fertilizer for onions?
Compost at planting and a nitrogen-rich fertilizer during early growth.
When should I stop fertilizing onions?
When the bulbs begin to swell and the neck starts to soften.
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Muhammet Elma
TarlaTapan guides focus on practical, field-tested growing advice. Corrections and suggestions are welcome at info@tarlatapan.tr.