Success in Growing and Harvesting Leek: Remember leek is a long season crop. There is NO rush to get seeds sown NOW! There are 2 types of leeks dependingon when you wish to harvest. Early to Mid Season ( sow Feb to early March) and Mid to Late season (sow Mid February to late March). Unless growing for exhibition then sowing starts December and early January! Do not plant in nitrogen rich soil (especially if the area had grass clipping worked into the soil earlier in the year). Overcrowding as w