Do all seeds require light during germination?
Written by
Paul Reynolds
Reviewed by
Prof. Samuel Fitzgerald, Ph.D.The light requirements for germination vary significantly among different plant species. This important factor determines if a seed becomes active or remains dormant. Some seeds require light to germinate, while some require dark conditions. Understanding these differences will help prevent wasted effort and ensure successful germination.
Seeds that depend on light for germination have specialized photoreceptors, known as phytochromes, that can detect specific wavelengths of light, signaling germination. Lettuce seeds that are surface-sown require red light to signal germination; covering them with soil blocks blocks this signal. Seeds that prefer to germinate in darkness have inhibitors that will only degrade in darkness.
For Light-Dependent Seeds
- Surface sowing: Press seeds into soil without covering
- Transparent covers: Use plastic domes for humidity and light penetration
- Grow lights: Position 2-4 inches above trays for 14 hours daily
For Darkness-Preferring Seeds
- Planting depth: Bury seeds 2-4 times their diameter
- Opaque covers: Use cardboard or fabric until sprouts emerge
- Dark germination: Start seeds in dark cabinets or covered trays
Monitoring & Adjustment
- Daily checks: Inspect for sprouting signs every morning
- Light meters: Measure intensity at soil level (200-400 μmol/m²/s ideal)
- Gradual exposure: Introduce light slowly for darkness-started seedlings
High-intensity light conditions can cause considerable delays when propagating seedlings. In some cases, light-dependent seeds may take weeks longer to germinate if they have not been exposed to illumination. Additionally, seeds that prefer nocturnal or shade conditions may develop weakly under bright conditions. All of these problems will negatively affect vigor. However, proper light placement can remedy most of these germination challenges.
Variation in sunlight based on geography will influence germination. Regions with cloudy skies will require supplemental lighting, whereas sunny areas with sensitive seeds will need shading. Adjust your germination techniques according to your specific growing conditions. Use inexpensive light meters to help track the number of hours of light that will hit your seeds daily.
The successful germination of seeds depends on light, as well as temperature and moisture. Light requirements work in conjunction with soil warmth. When the soil is cool, the seed will require more light. When soils are warm, they will germinate more quickly in the dark. Adjusting all the components will help achieve the best results, as close to balanced processes as possible.
Read the full article: Seed Germination Temperature Mastery Guide
