Bulb onion seed can be sown during March and April. Where large bulbs are required for exhibition sowings can be made in a greenhouse in late December and January. Onions require a sunny position and a well drained soil. Dig the area in autumn or early winter and incorporate garden compost. If the soil is acid add lime prior to planting. Firm the soil before sowing and apply a general fertilizer such as Growmore.
Early sowings can be made in a propagator, on a windowsill or in a greenhouse or conservatory maintaining a temperature of 15-20°C (60-68°F). Once the seedlings are large enough to handle transplant the seedlings individually into 7cm (3") pots maintaining a temperature of 10-13°C (50-55°F). Towards the end of March the plants can be hardened off in a cold frame or very sheltered spot. Depending on the weather conditions the young plants can be planted in their final position in mid April in the south of the country and about two weeks later in colder areas. For large onions space the plants 38cm (15") apart in the row and 60cm (24") between rows.
Spring sowings are made in rows spaced 30cm (12") apart. Once the seedlings are large enough to handle thin them to 10-15cm (4-6") apart.
The onions are ready for harvesting when the foliage turns yellow and topples over. On a dry day lift the bulbs and leave in the sun or under protection under protection in wet weather to dry, turning them two or three times. Depending on bulb size. Depending on bulb size drying can take one to three weeks. Once the bulbs have been dried they should be stored in a cool light place.