Once they are growing well,gently fill the trench with soil. Every few weeks, hoe another inch of soil into the trench up around the leeks until the hill is six to eight inches above the soil surface. This will give you nice, white leeks. Harvest as needed. They can be refrigerated for a few weeks, or stored in moist sand for two months.
Leeks are very good in soups, and there are many excellent recipes for chicken and leeks soup.
They also are good roasted in a medley with other root vegetables.