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.
Optimum Temperature for Germination: Use a heat mat to maintain steady temperatures of 68–72 °F (20–22 °C). Higher temps may reduce germination and produce weak seedlings.
Germination Time: 5 to 21 days
Sowing Instructions:
• Sow shallowly and cover lightly with vermiculite — seeds need light to germinate.
• Use grow lights to maintain 12–16 hours of light per day.
• Use a well-drained, low-nutrient medium (pH 5.8–6.2) indoors 4–6 weeks before last frost or direct sow outdoors after frost.
• Ideal media: 15–30% clay, enriched with complete fertilizer and micronutrients.
Watering:
• Keep soil evenly moist but not soggy — overwatering can cause rot.
• Provide good ventilation to prevent damping off.
Light Requirements:
Full sun – Zinnias thrive in warm, sunny spots.
Post-Germination Care:
• Grow on at 60–65 °F (15–18 °C) for 3–4 weeks. Temperatures below 60 °F (15 °C) can delay flowering.
• Thin seedlings to 6–12" (15–30 cm) apart for airflow and strong growth.
• Fertilize weekly at 100–200 ppm nitrogen using a balanced fertilizer.
• Use calcium nitrate to strengthen stems. Avoid excess ammonium or nitrogen, which causes soft, breakable stems.
• Apply magnesium sulfate (0.05%) 1–2 times to prevent deficiency.
• Apply iron-chelate if symptoms of iron deficiency appear.
• Harden off indoor seedlings gradually at 54–57 °F (12–14 °C) before transplanting outdoors.
Growing Tips:
• Great for beds, borders, and cut flower production
• For cut flowers: plant at 8–10" (20–25 cm) in rows or 9–12" x 12" (23–30 cm x 30 cm) in beds
• Disinfect greenhouse soil before planting; for outdoors, use loamy or sandy humus soil with good drainage
• Protect from wind and avoid frost exposure
• Deadhead spent blooms to encourage continuous flowering
Enjoy vibrant blooms from summer into fall!