Plant leeks in the spring, and late in the summer or fall. They are often harvested until the ground freezes in cooler climates.
When to Plant If you're starting your leeks by seed, sow them indoors 8-10 weeks before the last frost. Plant them 1/2 inch deep & thin to 1 inch apart when the seedlings are about 3-4| tall. Leeks prefer temperatures of 60-65 degrees when being transplanted. Harden them off by moving them outdoors as soon as your soil is workable.
How to Plant Plant leek seedlings 8-10 inches apart. Water well and make sure all of the roots are covered. Add additional soil around the plant as it grows to produce the long white stalks, that you so typically may see in culinary dishes.
When to Harvest Harvest your leeks when they reach a large, ideal size for cooking. Loosen the soil around the plant before pulling them, so you don't break them off. Allow your leeks to stay in the ground just before the ground freezes or use mulch or hay to over-winterize leeks if you live in milder climates.
Cut green tops off of leeks and store in a plastic bag in the refrigerator for up to two weeks.