Leeks are a close relative of the onion, but have flattened leaves and mildly flavoured stems instead of bulbs. The long, thick white stems are valued by gourmets for adding a sweet onion flavour to dishes. Growing Tips: As leeks require a very deep, rich soil, cultivate well prior to seeding and incorporate some compost or well-rotted manure. Seed may be planted directly in the garden in early spring or started indoors for an earlier harvest. Transplanted seedlings should be set in a 15cm (6”) deep trench that is gradually filled in as they grow. If seed is planted directly in the garden, hill soil around the leeks several times during the growing season, piling it higher each time.