Leeks (Allium ampeloprasum var. porrum) are a popular ingredient in soups, quiche and salads. Many people mistake leeks for green onions, but they differ in flavor and use. Only the white shaft of the plant is consumed, which measures up to 10 inches in length. Leeks require a long growing season. In northern climates start leeks in late winter to early spring indoors from seeds. In mild climates the plants are capable of surviving the winter and regrowing in the spring with very little care.
Leeks require a minimum of eight hours of full sunlight per day. They enjoy a slightly acidic soil with a pH of 6.0 to 6.8. Growth is achievable in alkaline soil conditions but is often stunted or slow. Well draining soil is ideal. The average growing time for leeks is 120 to 150 days but there are new cultivars available that can achieve full growth in only 90 days.
Transplants that have been successfully grown indoors will need to be hardened off prior to planting. Begin setting the plants outside for a period of five to seven days to toughen the plants up and allow them to adjust. Carry the plants back inside each night when the sun sets. The daytime temperatures must be above 45 degrees F. before setting out the transplants. The ideal age of a transplant is between 10 to 15 weeks old.
Plant transplants in rows that are located 36 inches apart. Each plant in the row should have a spacing of 6 inches between each other. Ideal spacing is important because of the high light requirements that leeks have. Sunlight must reach the foliage of the plant. Air circulation is also important to reduce the risk of possible fungal infections. Locate the transplants root system at least 6 inches deep within a furrow. As the plant grows add soil to the furrow. Soil should always be maintained right at the start of the leeks leaves. Take care when removing weeds and hoeing around leeks because their root system is shallow and easily damaged.
Fertilizing and Watering
Fertilize leeks at the time of planting with a 10-10-10 plant fertilizer. Fertilize again mid season using the same fertilizer to help supply the leeks with much needed nutrients. Leeks enjoy moist soil conditions but they should never be waterlogged. Watering once per week is sufficient.
Harvest leeks when their diameter is 1 inch. The plant should be firm to the touch. Simply pull the leeks from the ground. Wash them thoroughly and remove foliage. Because of the leeks outstanding frost tolerance many people mulch their leeks heavily and abstain from harvesting until late fall or even early winter. In milder climates leeks are grown year round.