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Leeks Seed Starting Tips

Leeks in row
Leek seedlings
Leek seedlings

Leeks are a cool- and cold-season crop.

There are two types of leeks: short-season leeks and long-season leeks. Long-season leeks which have thick, cylindrical stems–and keep long, and short-season leeks that have a thinner stem and don’t keep as well as long-season leeks.

Short-season leeks mature in as few as 70 days. Long-season leeks mature in about 120 to 170 days. Short-season leeks are harvested during the summer. Long-season varieties are harvested from late summer through winter.

Leeks are best started indoors in late winter–about 12 weeks before the last frost–and then transplanted to the garden about a week after the last spring frost.

Sowing and Planting Leeks

  • Grow leeks from seed or transplants.
  • It’s best to start leeks from seed indoors 12 to 4 weeks before the last spring frost; later, set out transplants in spring at least 1 week after the last frost when seedlings are the thickness of a pencil
  • In mild-winter regions and where the summers are hot, set out transplants in autumn.
  • Sow seed indoors in flats or individual pots; sow seed ⅛ inch (3 mm) deep 1 inch (2.5 cm) apart.
  • Set out transplants when seedlings are 6 to 12 inches (15-30 cm) tall; space plants 2 to 4 inches (5-10 cm) apart in trenches 5 inches (13 cm) deep or drop seedlings in a hole about 6 inches deep leaving just one or two leaves above the surface.
  • Space rows 12 inches apart.
  • Start seed in a potting mix then transplant to loose, fertile soil in the garden. Adding aged compost to planting beds in advance of sowing will feed the soil and aide moisture retention.
  • Seed will germinate in 8 to 16 days at an optimal temperature of 70°F (21°C) or thereabouts.
  • Optimum soil temperature to grow leeks is 70°F (21°C).
  • Leeks prefer a pH range of 6.0 to 6.8.
  • Grow leeks in full sun for best yield.
  • Keep the soil evenly moist during growth.
  • Keep the planting beds free of weeds to avoid competition for moisture and nutrients.
  • Avoid planting leeks where onions or garlic have grown recently.
  • Fertilize with an organic fertilizer such as fish emulsion at half strength.
  • Common pest enemies include thrips and root maggots.

Interplanting: Plant leeks with beets, carrots, celery, garlic onions, and tomatoes.

Container Growing Leeks: Grow leeks in a container at least 10 to 12 inches (25-30 cm) deep.

Leek Planting Calendar

  • 4-3 weeks before last spring frost: start the seed of long-season varieties indoors for fall and winter harvest.
  • 8-6 weeks after the last spring frost: transplant seedlings into the garden for winter harvest.
Leeks growing
Leeks require 70 to 170 days to come to harvest and grow best where the temperature ranges from 45° to 85°F.
  • ‘American Flag’ (120 days) and ‘Giant Musselburgh’ (150 days) are favorites.
  • ‘King Richard’ (75 days) is early maturing.
  • ‘Blue Solaise’ is sweet-tasting; ‘Argenta’.
  • ‘Unique’, ‘Tardona’ and ‘Nebraska’ are cold hardy.

Botanical Name: Allium porum

Leeks are a member of the Alliaceae also called Lilliaceae family, other members of this family include onions and garlic.

Related Articles:

How to Grow Leeks

Troubleshooting Onion Family Crop Problems

Written by Stephen Albert

Stephen Albert is a horticulturist, master gardener, and certified nurseryman who has taught at the University of California for more than 25 years. He holds graduate degrees from the University of California and the University of Iowa. His books include Vegetable Garden Grower’s Guide, Vegetable Garden Almanac & Planner, Tomato Grower’s Answer Book, and Kitchen Garden Grower’s Guide. His Vegetable Garden Grower’s Masterclass is available online. has more than 10 million visitors each year.

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