When to plant
Start seeds indoors in late winter (10–12 weeks before last frost) or plant onion sets in early spring as soon as the ground can be worked. Onions need a long season (100–120 days) and prefer cool weather for top growth before switching to bulbing as days lengthen.
Soil & site
Onions need fertile, well-drained, loose soil. pH 6.0–7.0. Work in compost and a balanced fertilizer before planting. They form bulbs near the soil surface — don't plant in heavy clay which restricts bulb expansion.
Feeding
Nitrogen-rich fertilizer early in the season encourages leafy top growth (which feeds the bulb). Switch to a phosphorus/potassium fertilizer in midsummer when bulbs begin to size up. Stop feeding 4–6 weeks before harvest to harden the bulb.
Common problems
Onion fly maggots (yellowing, collapsing plants — row cover from planting). Thrips (silvery streak damage — neem oil). White rot (see garlic). Bolting from temperature swings — vernalisation causes early bolting in some varieties.
When to harvest
Onions are ready when about half the tops have fallen over naturally. The outer wrappers should be dry and papery. Don't wait for all tops to fall — this can indicate disease. Stop watering 2 weeks before harvest to encourage curing.
How to harvest
Use a fork to loosen soil before lifting. Avoid bruising — any injury shortens storage life significantly. Spread or hang in a warm, dry, ventilated location for 2–4 weeks to cure. The neck must be completely dry before storing. Braid softneck varieties or cut tops of hardneck to 2–3 cm.
Storage & use
Properly cured onions store at cool room temperature in a mesh bag or in old pantyhose (tied in knots between each onion) for 3–6 months. Keep dry and dark. Don't store near potatoes — they emit ethylene gas that shortens each other's life.
Companion planting
Onions repel many pests but inhibit legumes. Keep away from beans and peas.
Useful for growing onion
A few things that make this one easier — chosen for this plant, not a generic list.
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