Optimum Temperature for Germination:
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 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!