Allium porrum, commonly known as leek, is a biennial vegetable belonging to the onion family (Alliaceae), native to southern Europe, North Africa, and western Asia. Leek seeds require warm soil temperatures (70°F/21°C optimal) for reliable germination and do not need cold stratification, unlike many other Allium species. The species is relatively easy to grow from seed when provided with consistent moisture, adequate light after emergence, and cool daytime temperatures of 55-65°F for healthy seedling development.
Before sowing
No pre-treatment needed — sow directly.
Cold stratification is not required for leek seeds. Optional: Store seeds in airtight containers in refrigerator to preserve viability, as leek seed viability deteriorates rapidly after one year.
Sowing
What to expect
Tips
1) Maintain soil temperature at 70°F (21°C) for fastest germination; seeds will germinate slower (but still viable) at 50°F or in temperature ranges of 45-90°F. 2) Provide bright light (12-16 hours daily) immediately after seedling emergence to prevent leggy growth. 3) Keep substrate moist but not waterlogged; provide humidity with propagation dome initially, then remove after germination. 4) Thin seedlings to 0.5-1 inch spacing when 2-3 inches tall to prevent overcrowding and competition. 5) Use fresh seed annually as viability deteriorates rapidly; store in airtight containers in refrigerator. 6) Optional heat mat (75-85°F) accelerates germination; cool to 65-70°F after emergence. 7) Seedlings are ready to transplant when 6-8 inches tall with stem thickness similar to pencil width (approximately 10-15 weeks after sowing).
Sources: Cambridge Journal of Seed Science Research, University of Nebraska Extension, High Mowing Seeds, West Coast Seeds, GardenFocused.co.uk, Missouri Botanical Garden
