Onions are in almost every meal on Earth, and learning how to grow onions means you'll never run out. The crucial secret most beginners miss: onions bulb according to day length, so choosing the right type for your latitude matters more than anything else you do.
Onion Quick Facts
| Factor | Details |
|---|---|
| Difficulty | Easy–Moderate |
| Days to harvest | 90–150 days (seed), 80–100 (sets) |
| Sunlight | 6+ hours full sun |
| Soil pH | 6.0–7.0 |
| Spacing | 10–15 cm (4–6 in) apart |
| Ideal temperature | 13–24°C (55–75°F) |
Choose the Right Onion for Your Latitude
- Long-day onions — need 14–16 hours of daylight to bulb. For latitudes above 35° (northern USA, UK, northern Europe, Canada).
- Short-day onions — bulb at 10–12 hours of daylight. For latitudes below 35° (southern USA, North Africa, South Asia, northern Australia).
- Intermediate (day-neutral) — flexible, for latitudes 32–42°.
Plant the wrong type and you'll get lush leaves but tiny bulbs.
When to Plant Onions
| Region | Method & Timing |
|---|---|
| Northern temperate | Sets or transplants in early spring (March–April); seeds indoors in winter |
| Southern temperate | August–October |
| Subtropical/South Asia | Short-day types sown October–December |
| Mild-winter areas | Autumn planting for overwintered early crops |
Sets vs Seeds
- Sets (small dormant bulbs): easiest and fastest, great for beginners, but slightly more prone to bolting and fewer varieties.
- Seeds: cheapest, most variety choice, best storage onions — but add 4–6 weeks and need early indoor sowing.
How to Plant Onions: Step by Step
- Prepare a sunny bed with compost and good drainage.
- Plant sets 2 cm (1 in) deep, pointed end up, 10–15 cm apart.
- For seedlings, transplant when pencil-thick at the same spacing.
- Keep weed-free — onions' thin upright leaves compete very poorly with weeds.
Onion Care
- Watering: Regular, shallow watering; stop watering once tops begin falling over near harvest.
- Feeding: Nitrogen feed every few weeks early on; stop when bulbing starts.
- Bolting: If a flower stalk appears, harvest that onion and use it fresh — it won't store.
When to Harvest Onions
The signal is unmistakable: the tops yellow and flop over naturally. Then:
- Stop watering.
- A week later, lift bulbs gently on a dry day.
- Cure in a single layer in a dry, airy spot for 2–3 weeks until necks are papery.
- Store in mesh bags somewhere cool and dry — good storage onions keep 6+ months.
Health Benefits of Onions
Onions are rich in quercetin, an anti-inflammatory antioxidant, plus vitamin C, B6, and prebiotic fibers that feed beneficial gut bacteria. The compounds that make you cry (sulfur compounds) are linked to heart-health benefits.
Common Onion Problems
| Problem | Cause | Fix |
|---|---|---|
| Small bulbs | Wrong day-length type, weeds, late planting | Match type to latitude; plant early |
| Bolting (flowering) | Cold snaps or stress | Use heat-treated sets; consistent care |
| Soft, rotting necks | Harvested too wet or poor curing | Cure fully before storage |
| Yellow, wilted leaves | Onion fly maggots | Crop rotation; insect mesh |
FAQ
Can I grow onions from a sprouting kitchen onion? It will produce green shoots and eventually flower — good for green onions, but it won't form a new big bulb.
How many onions grow from one set? One set grows one onion. Plant as many sets as onions you want.
Can onions grow in containers? Yes — a wide container 20 cm (8 in) deep works; space bulbs 10 cm apart.
Why are my onions all leaves and no bulb? Almost always wrong day-length variety for your latitude, or too much late nitrogen.
Check exact onion planting dates for your country on our crop calendar.
Frequently Asked Questions
Can I grow onions from a sprouting kitchen onion? +
It will produce green shoots and eventually flower — good for green onions, but it won't form a new big bulb.
How many onions grow from one set? +
One set grows one onion. Plant as many sets as onions you want.
Can onions grow in containers? +
Yes — a wide container 20 cm (8 in) deep works; space bulbs 10 cm apart.
Why are my onions all leaves and no bulb? +
Almost always wrong day-length variety for your latitude, or too much late nitrogen.