How to grow onion
Overview
Onion is a versatile vegetable grown for its pungent bulbs or green stems. It thrives in full sun with consistent moisture and benefits from a nitrogen-rich start followed by potassium to swell bulbs.
Varieties
- Brown Spanish — A reliable, large brown onion for storage, popular in temperate zones.
- Red Torpedo — A sweet, elongated red onion ideal for salads, suited to subtropical areas.
- White Lisbon — A quick-growing spring onion for green stems, good for all zones.
- Creamgold — A golden, mild onion with good storage, bred for Australian conditions.
Soil Preparation
Onion prefers a pH of 6.0–7.0 in loose, well-drained soil. Enrich with compost or well-rotted manure before planting. Avoid fresh manure to prevent disease.
Growing Guide
Sow onion seeds 6 mm deep in rows 30 cm apart, thinning to 10 cm between plants. Choose a sunny, well-drained site with rich soil; avoid heavy clay. For bulbs, start in autumn in warm zones or spring in cool zones. Water regularly but do not let the soil become waterlogged.
Sowing
Sow seeds 6 mm deep, 10 cm apart in rows 30 cm apart. Germination takes 7–14 days at 15–20°C. Direct sow is best; transplanting can be done but may slow growth.
Care
Feed every 3–4 weeks with a nitrogen-rich fertiliser until bulb swelling begins, then switch to a potassium-based feed. Remove flower stalks promptly to redirect energy to the bulb. Keep beds weed-free to reduce competition.
Companion Planting
Onion grows well with carrot, beetroot, lettuce, and strawberry. Avoid planting near beans and peas, which can reduce onion growth.
Common Pests & Risks
Thrips cause silver streaks on leaves; control with insecticidal soap or neem oil. Downy mildew appears as yellow patches; improve air circulation and avoid overhead watering. Onion maggot is rare but can be deterred with crop rotation.
Harvesting
Harvest when tops turn yellow and fall over, typically 4–5 months after sowing. Lift bulbs on a dry day and cure in a warm, airy spot for 2 weeks before storing.
In the Kitchen
Use fresh in salads, cooked in stews, or caramelised for sweetness. Store bulbs in a cool, dark place for months. Green stems can be used as spring onions.
Troubleshooting
Yellow leaves: overwatering or poor drainage; reduce water and improve soil. Brown edges: underwatering or heat stress; increase moisture. Bulbs small: too much nitrogen late; switch to potassium. Bolting: temperature stress or early planting; choose right season. Soft bulbs: fungal rot from wet soil; ensure drainage.