Exceptionally hardy, leeks are best started from seed indoors in April in seed starting mix. Then plant them out in the garden in May and harvest them starting in the fall.
Leeks are also more successful in heavier soils than onions.
Plant leek transplants two inches apart in rows 18 inches apart. Then push soil around the edge up to the first leaf notch to blanch or whiten the stems. Or plant leek transplants into trenches three to four inches deep. As the leeks grow taller, fill in the trenches in stages until the trenches are completely filled in. Or, plant leek seeds directly into a well worked garden bed.