Onion

The onion (Allium cepa) is the world's most widely cultivated bulb vegetable, prized for its pungent, layered flesh and extraordinary culinary versatility. Varieties range from golden-skinned storage types to vivid red and mild fresh-eating forms. It thrives in full sun in well-structured, humus-rich soil and requires consistent moisture and excellent weed control, as its fine roots compete poorly against weeds. In Nordic conditions, indoor pre-cultivation is strongly recommended to ensure bulbs develop fully before the end of the growing season.

Growing

Sow seeds about 1 cm deep indoors or in a cold frame when indoor temperatures can be maintained at 20–25 °C for germination. Once seedlings emerge, move to a bright, airy position kept below 15 °C to prevent premature bulbing — the plants must not mistake cool indoor warmth for full summer. Clip leaves back to about 6 cm periodically during pre-cultivation to encourage sturdier stems. After around 10 weeks, harden off transplants and plant out once nights stay reliably above 5 °C and all frost risk has passed, setting plants 10 cm apart in rows 25–50 cm apart, no deeper than they stood in the tray. Alternatively, direct-sow into warm outdoor soil in a dense strip to produce sets for the following year.

Care

Water consistently but avoid waterlogging; onions in dry soil stall and split when rains return. Apply a balanced fertiliser at planting and a nitrogen-rich feed early in growth; reduce feeding once bulbs begin to swell. Keep the bed scrupulously weed-free throughout — onion foliage provides little canopy cover and even modest weed competition significantly reduces yields. No staking required. If any plants send up flower stalks, remove them promptly to keep energy directed into the bulb.

Harvest

Bulb onions are ready when the foliage naturally bends over and begins to dry. Do not bend the tops manually; wait for them to fall on their own, which signals that the neck has closed and curing can begin. Lift bulbs carefully with a fork, brush off loose soil, and allow them to cure in a warm, airy spot until the outer skins rustle and the neck is fully dry. Spring onions can be pulled as soon as they reach pencil thickness, at any stage up to full bunching size.

In the kitchen

Onions are a foundation of virtually every savoury cuisine: raw in salads and salsas for sharp bite, slowly caramelised for deep sweetness, fried for crunch, or simmered into soups, stews and sauces. Red varieties are mild enough to use raw in slaws and pickles. Spring onions add fresh allium flavour as a garnish or stir-fry ingredient. The papery outer skins can be used to add colour and depth to stocks.

Storing

Fully cured dry-skin onions store for 3–8 months in a cool (0–5 °C), dry, dark and well-ventilated location — a net bag or slatted crate works well. Do not store near apples or potatoes. Red and mild varieties generally store for a shorter period (2–3 months) than firm, pungent yellow types. Chopped raw onion keeps refrigerated in an airtight container for up to 5 days. Sliced or whole onions can be frozen (no blanching needed) for up to 6 months for use in cooked dishes.