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.
Seed Treatment
Step 1: Soak seeds in room-temperature water for 12–24 hours—before cold stratification.
Step 2: Cold stratify by mixing seeds with moist sand or peat moss and refrigerating at 1–4 °C (35–40 °F) for 60 days.
When to Sow
Outdoors (natural stratification)
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Sow in the fall to allow outdoor cold stratification over winter.
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Surface-sow into a partially shaded to full-sun location with moist, well-draining soil. Light is required for germination—do not cover seeds.
Indoors (controlled germination)
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Start seeds 6–8 weeks before the last frost, after completing stratification.
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Use seed trays with a well-draining, moist mix.
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Light: Seeds require light to germinate—surface sow and do not cover.
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Use grow lights to maintain 12–16 hours of light per day.
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Use a heat mat to maintain steady temperatures of 18–24 °C (65–75 °F).
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Germination typically occurs 2–6 weeks (14–42 days) after stratification.
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After germination, gradually acclimate seedlings (“harden off”) before transplanting outdoors.
Humidity: Use a humidity dome or clear cover to maintain consistent moisture during germination. Open briefly once per day for fresh air and to reduce mold risk. Remove entirely once seedlings emerge.
Post-Germination Care
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Transplant spacing: Thin or transplant seedlings to 30–45 cm (12–18 in) apart.
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Soil: Rich, moist with pH 6.0–7.0.
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Light: Full sun to partial shade.
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Water: Keep soil consistently moist.
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Mature size: Reaches about 90–120 cm (3–4 ft) tall.
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Fertilizer: Apply balanced organic feed in early spring.
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Pruning: Cut back in late fall or early spring to promote healthy regrowth.
Growing Tips
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Prefers rich, moist soils—ideal for damp spots or near water features.
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Hardy in zones 3–7 (up to 9 in mild climates).
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Attracts pollinators with airy pink-white blooms in mid-summer.