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
Soak seeds in warm water for 2–4 hours before sowing.
GA₃ (gibberellic acid) can be used at 250 ppm for 12–24 hours to boost germination, but only if you're experienced—incorrect use can destroy seeds.
Best Time to Sow
Indoors: Start 6–8 weeks before your last frost date
Outdoors: Sow after the danger of frost has passed, once soil warms to at least 18°C (65°F)
Germination Conditions
- Optimum Temperature: 18–22°C (65–72°F)
- Light Requirements: 12–16 hours of light per day—use grow lights
- Do Not Cover Seeds: Light is required for germination. Press gently onto moist seed-starting mix.
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.
Germination Time: 7 to 30 days
After Germination
- Thin seedlings when 5–7 cm (2–3") tall
- Harden off before transplanting outdoors (gradually expose to outside conditions over 5–7 days)
- Space 15–20 cm (6–8") apart in full sun
- Water regularly but avoid overwatering—soil should be well-draining
Growing Tips
- Deadhead spent blooms to encourage continuous flowering
- Prefers moderately fertile, slightly acidic to neutral soil (pH 6.0–7.0)
- Mulch to retain soil moisture and reduce weeds
- Suitable for borders, containers, and cottage gardens
- Attracts butterflies and pollinators
Sun Requirements: Full sun (at least 6 hours daily)
Bonus: Heat-tolerant and deer-resistant once established
With a little attention during germination, Phlox drummondii will reward you with a stunning, long-lasting floral display!