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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.

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