Light-Dependent Germinator
Light-dependent germinators are plants whose seeds only germinate when exposed to light. When sowing, they should not be covered with substrate, or only with a very thin layer, as darkness prevents germination. Light activates special plant hormones (phytochromes) in the seed that trigger the germination process.
Typical light-dependent germinators include many fine-seeded species, among them:
- Common Snapdragon (Antirrhinum majus)
- Poppy (Papaver)
- Thyme (Thymus vulgaris)
- Basil (Ocimum basilicum)
- Bellflower (Campanula)
- Corn salad / lamb's lettuce (Valerianella locusta)
Sowing and special considerations
Light-dependent germinators are scattered onto moist substrate and only lightly pressed down. To keep the delicate seeds from drying out or being washed away, they can be covered with a very thin layer of fine quartz sand or vermiculite. Both materials let light through and keep moisture evenly distributed.
This covering offers several advantages: it protects the seeds not only from drying out, but also from being eaten by birds and from being washed away when watering. When moistening, always use a very fine spray so as not to displace the seeds.
Direct sowing in the bed can be difficult for light-dependent germinators, as sun, rain and wind quickly lead to drying out or displacement of the seeds. Germination is therefore often more successful in seed trays in a bright but not fully sunny spot with constant moisture.
Why light-dependent germinators need light
The light stimulus serves plants as a natural signal for favourable germination conditions. Light-dependent germinators usually originate from open, sunlit habitats such as meadows, roadsides or rocky ground, where their seeds lie on the surface. Only in the presence of light do they "recognise" that they are not buried too deep in the soil and that sufficient warmth, oxygen and space to grow are available.
The inhibition of germination in darkness protects the seed from germinating in an unsuitable location, from which it would not be able to reach the surface through the soil layer above it. In this way, light-dependent germinators ensure that their seedlings only grow where they have the best chances of survival, a clever adaptation to changing environmental conditions.