Onion

The onion (Allium cepa) is also known as the "garden onion" or "bulb" onion. Above ground, the onion shows only a single vertical shoot; the bulb grows underground, and is used for energy storage, leading to the possibility of confusion with a tuber, which it is not. Allium cepa is known only in cultivation, but related wild species occur in Central Asia.

Location
Onions prefer a sunny, well drained site although a moist site can be tolerated if grown in ridges. Avoid bulky soil, but again this can be tolerated if conditions are managed.

Soil
Soil should be fertile, but excessive nitrogen will delay maturity so avoid freshly manured soil. Manure should be dug in 2 months prior to planting. Acidic soil should be treated with lime to neutralise its pH.

Sowing
Sow seeds in modules in late January and kept indoors at temperatures of 13°C (55°F) to 35°C (95°F). You can plant up to 5 seeds in each module, once transplanted plants will push apart. Alternatively sow seeds outdoors in February-March. For a continual supply; make a second sowing in August for a crop ready in June the following year.

Transplanting
Transplant seedlings in early April.

Planting Sets
Plant onion sets in Spring so that the tip of the bulb is just showing above the soil.

Weeding
Since onions do not produce dense foliage to shade the surrounding earth from weeds; regular weeding is essential or plants will soon be overrun with competing plants.

Bolting
Bolting can be an issue with some onions depending on variety and growing conditions. If a flower stalk begins to form, cut it off.

Harvesting
Onions are ready to harvest once foliage starts to turn yellow. Leaves should not be folded to speed this process up. Lay harvested onions in a warm dry place for 2 weeks to dry out. Onions that develop a thick neck should be used immediately as these do not store well and are prone to neck rot.

Storing
Once foliage is completely dry, store onions in a dark, cool, dry place either by packing in boxes or in plaits. Onions should keep for 3-6 months depending on variety.