We all know that most plants need light for photosynthesis. But what about seeds before green shoots and leaves emerge? What seeds need light to germinate – and why?
The process of seed germination requires the right temperatures, moisture levels, and oxygen. But what you might not know is that some seeds need light to germinate too.
Most seeds do not need light to sprout, and some require dark conditions. But some seeds do need light to break dormancy and will not germinate without it.
Why Some Seeds Need Light for Germination
Larger seeds on the whole don’t need light to germinate – and some actively need dark conditions. Those that require light tend to be on the smaller side, as plants with tiny seeds often require sunlight as they don’t contain all the energy required.
Smaller seeds need the energy from sunlight or grow lights to break dormancy because they do not contain sufficient food reserves to push up from deeper soil to reach the light.
Since these smaller seeds do not have large reserves, the requirement of light for successful germination is a kind of safety mechanism, which prevents them from trying to sprout too far underground.
Light breaks dormancy in these seeds by triggering photoreceptors. This suppresses the production of abscisic acid, which maintains the dormancy of a seed, and causes gibberellins hormone to be released, which allows for germination.
It is also common for flowering plants that self-seed to be those that require light for germination. Likely, self-seeding plants have seeds of this kind because the seeds will drop from the plant and will germinate on the soil surface around their parent plant.
Seeds that Need Light for Germination
As gardeners, we need to know which seeds need light for germination as this will have an impact on the process of sowing these seeds. This is true whether you are sowing directly into garden beds, or indoors, either to transplant outdoors later or to grow indoors throughout the year.
Vegetable Seeds
Most vegetable seeds do not require light for germination, and some, especially larger seeds like beans, for example, will germinate better when light is excluded and they are buried a little more deeply in the growing medium.
But a few do require light for successful germination. Lettuce is one example of this, and celery and carrots also need some light for germination.
Need some light.
Onion seeds are also covered only lightly, but these do not need light for germination. And though other seeds may also only be covered lightly with your growing medium, light is not essential for them at this stage of the process either.
Though the list is not long when looking at vegetable seeds that need light to germinate, remember that all vegetables will need light after green shoots and leaves appear. Seedlings will need to be placed in as bright a spot as possible soon after germination has taken place.
Herb Seeds
Some herb seeds also need light for germination to take place. Some herbs that are in this category are:
Flower Seeds
The list of flower seeds that require light for germination is a lot longer than the lists of edible crops above. So if you are sowing flower seeds alongside your vegetables and herbs then this is an important consideration.
Some of the flower seeds that need light to germinate are:
- Ageratum
- Alyssum
- Angelica
- Antirrhinum
- Begonia semperflorens
- Browalia
- Calceolaria
- Coleus
- Columbine
- Exacum
- Ficus
- Gaillardia
- Gerbera
- Gloxinia
- Impatiens
- Jacobaea maritima
- Lobelia
- Nicotiana
- Osteospermum
- Petunias
- Platycodon grandiflorus
- Papaver
- Pelargonium
- Portulaca
- Primula veris (most)
- Salvias
- Streptocarpus
- Torenia
- Xerochrysum bracteatum
Though, of course, this is not a complete list.
How to Sow Seeds
When seeds need light for germination, this means that they should be sown on the surface of your growing medium, or covered only very lightly with a delicate covering of the medium that still lets some light through.
Which of these options will be correct depends on specifically what you are growing. Remember, seeds have different requirements, and as well as considering light you will also need to think about the temperatures required, and provide a medium that is moist enough, and aerated.
Whenever you are sowing seeds it is important to understand the recommended sowing depth for the particular plant and variety that you are trying to grow.
All seeds will germinate best when planted at a certain depth. Seeds that need light will of course be at the shallowest end of the spectrum, while those that need it to be dark and moist are sown more deeply.
Even when seeds do need light for germination, a light covering may often be beneficial to prevent the seeds from drying out too much, or to ensure that temperatures do not drop too low.
Outdoors, a light covering will also protect seeds from being eaten by birds or other wildlife, though of course, this is not a particular concern in most cases when growing indoors.
