Leek Growing Information Allium porrum Transplant: Sow in early spring and through summer (if overwintering in mild areas). Start in trays at ½” depth. Soil temperature for germination is 50-80° F. Transplant when starts are 7-8” tall and pencil thick. Plant deeply up to 1st leaf notch. Spacing: 6” apart in rows that are 12-24” apart. Growth needs: Grows best with high organic matter in fertile soil. For long, white shanks, hill dirt around the plants 2-3 times as they grow. Harvest: When diameter and height are at desired size, use an undercutter or fork to loosen roots. Storage: Can store cleaned in boxes at 32° F at 95% relative humidity, or in a root cellar with moist soil for multiple weeks. Can also be left in field in mild climates if temperatures are cooler and near freezing.