Leeks are a bit more labor-intensive to grow than their allium cousins, but when you see the price for them in the stores, you may decide a little extra digging is worth it. The goal is to create as long and thick a white shaft as possible, and you achieve that by either digging a furrow in which to plant the starts or by mounding the starts once planted (or both). Furrows should be at least six inches deep, then plant the starts in the furrow six inches apart. Note: the tops, called flags, grow in a single plane, so if possible, plant the starts with the width of the flags extending into the rows and not into the plant next to it. As the plants grow, fill in the furrow with soil. Alternatively, plant the starts at normal soil level, then mound with soil or compost as the plant grows. 

Harvest leeks when the white shanks are around an inch in diameter.