Sow in Autumn thinly, 5mm deep, in rows. Cover with fine soil or compost and keep moist. Thin seedlings early to 2cm and later to 10cm apart. Allow 30cm between rows. Prepare the soil well by adding organic material and a pre-planting fertiliser. Onion varieties vary in maturity so you can have a crop for many months of the year. Grow in a fine rich soil and an open sunny position. Seedlings emerge 10-14 days.