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 lukewarm water for 2–4 hours before sowing.
Do not cover seeds with soil—light is needed to germinate.
Best Time to Sow
Indoors: Start seeds indoors 8–10 weeks before your last frost date.
Can be sown year-round in a controlled environment.
Germination Conditions
Temperature: 70–75°F (21–24°C)
Light Requirement: Use grow lights to maintain 12–16 hours of light per day.
Germination Time: up to 21 days
How to Sow
- Press seeds gently onto moist seed-starting mix; do not cover with soil.
- Mist the surface.
- Keep in a warm, well-lit area with consistent humidity.
Watering
Keep soil consistently moist, not soggy. Mist to avoid washing away tiny seeds.
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.
Post-Germination Care
- Provide bright light or grow lights for 14–16 hrs/day to prevent leggy growth.
- Transplant when seedlings have 2–3 true leaves.
- Harden off before moving outdoors by gradually exposing to outdoor conditions.
Growing Tips
- Pinch tips regularly to encourage bushier growth.
- Coleus is frost-sensitive: bring indoors or overwinter as a houseplant in cold climates.
- Ideal as a border plant, container filler, or indoor color accent.
USDA Zones: Annual in zones 2–9, perennial in frost-free zones 10–11
Height: 12–36 in (30–90 cm) depending on variety
Light Needs: Partial shade to full shade outdoors; bright indirect light indoors