For optimal germination rates, initiate seed propagation indoors under controlled conditions—unless the species exhibits a high sensitivity to root disturbance. This approach allows precise regulation of temperature, humidity, and light, improving germination consistency and seedling viability. Do not skip any recommended seed treatments, as they are essential for uniform and successful germination.
Keep soil evenly moist during germination. DO NOT LET IT DRY OUT—once seeds begin absorbing water (imbibition), drying can kill the seed embryo, and even brief dryness after sprouting can kill seedlings.
Seed Treatment
Soaking: Soak seeds in room-temperature water for 8–12 hours. Drain and sow immediately.
(No cold stratification or scarification required.)
When to Sow Indoors: Sow indoors 8–10 weeks (56–70 days) before your last expected frost date.
Optimum Germination Temperature: 18–22 °C (64–72 °F). Use a heat mat to maintain steady temperatures if necessary.
Germination Time: up to 21 days
Light Requirements for Germination: Light is not required for germination. Cover seeds lightly with soil. Once seedlings emerge, use grow lights to provide 12-16 hours of light per day.
How to Sow Indoors
-
Use seed trays or small pots with fine, well-draining seed-starting mix
-
Sow seeds 0.5–1 cm (¼–⅜ in) deep
-
Gently firm soil and water thoroughly
-
Humidity: Use a humidity dome or clear cover to maintain consistent moisture during germination. Open the dome BRIEFLY once per day to allow fresh air in and reduce mold risk. Remove the dome entirely once seedlings emerge.
-
Place in a warm location within the optimal temperature range
Post-Germination Care
-
Move seedlings to bright light immediately after emergence
-
Keep soil consistently moist but not waterlogged
-
Once seedlings are sturdy, transplant outdoors after hardening off
-
Final spacing: 15–20 cm (6–8 in) between plants
-
Plant type: Biennial grown as an annual vegetable
-
Mature height: 30–60 cm (12–24 in)
Growing Tips
-
For long white stems, gradually hill soil up around the plants as they grow
-
Leeks prefer cool weather and tolerate light frost
-
Grow in deep, fertile soil rich in organic matter
Water regularly—uneven moisture can reduce stem quality
More guides at: bloomoutlet.com/seed-guides