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.
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.
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.
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.