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Large American Flag Leek Guide

Large American heirloom leeks are a popular variety with excellent yields. Pick when the stalks are 15-18 inches in length. This variety has a mild creamy onion flavor. Potato leek soup anyone?


Leeks are hardy and grow best in cooler weather between 55°F-75°F. They do great in containers and small gardens. Bank on Seeds recommends transplanting.

If Direct Seeding

  • Direct seed outside 2 weeks before the last frost date; or
  • Direct seed into a container 8-10 inches deep and wide anytime of the year. It can be placed outside when the temperature is between 55°F-75°F; or

If Transplanting

Begin the growing season early and start the leek seeds indoors in trays or pods 6-8 weeks before the last frost date. Germination is best and fastest between 75°F-85°F. It can be transplanted outside 8 weeks later.

Sow seeds 1/4 inch deep and 6 inches apart with rows spaced 12 inches apart. Germination will take 5-10 days. Thin seedlings to 6 inches apart when they start competing for space.


Leeks like well-draining, fertile soil with lots of organic matter. They also like full sun and cool growing conditions but will tolerate partial shade. Water regularly to keep the soil evenly moist and do not let it dry out fully. Check the top 2-3 inches of soil and if it is dry, then water it.

Apply mulch to the top of soil to retain moisture, regulate temperature and deter weeds. Leeks usually do not require extra fertilizer but if needed, use 10-10-10 or a nitrogen heavy fertilizer or aged compost.


Days to maturity take 75-105 days. Harvest when the stem of the plant is 1-2 inches wide. If the soil is loose enough you can gently twist and pull the leek out or dig around the base, then pull it out.


Leaf miners, onion maggots, thrips– neem oil, crop rotation, remove and destroy affected plant, insecticidal soap

Rust, leaf blight, mildew, white rot – fungicide, do not water from overhead, let dry between watering, keep free of weeds, rotate crop every 3 years

*Plant leeks with beets, carrots, celery, garlic, and onions. Avoid planting with beans and peas.*