Most seeds germinate in dark, damp conditions and need to be covered with a suitable depth of topsoil. However, some seeds need light for successful germination.
In the vegetable patch, only varieties of lettuce, Cape Gooseberry, Tomatillo and the Asian greens Seakale and Shiso are ‘light responsive’, but a number of herb and flower species also require light for germination. These include: Angelica, Anise, Arnica, Ashwaganda, Caraway, Catnip, Chamomile, Chervil, Dill, Echinacea, Elecampagne, Evening primrose, Feverfew, Gazania, Lady’s Mantle, Lemon Balm, Mignonette, Rosemary, Summer and Winter Savory, Valerian, Watercress, Wormwood and Yarrow.
Sowing seed for these plants can cause difficulties as the seed is merely pressed into the soil surface and require close attention to prevent them drying, resulting in germination failure. Or, they are scattered on the surface of a punnet where they can be easily washed into clumps at the edge of the punnet despite careful watering.
A way to avoid problems with these seeds is to fill a punnet with damp seedling mix and then cover the surface of the punnet with a single layer of gravel or small pebbles. Then sprinkle the seeds sparingly over the gravel and water very gently, being careful not to flood the surface. The gravel provides crevices for the seed to settle while still allowing them to receive light, and also helps to keep the growing mix damp for germinating seeds.