Light Matters: Why Some Seeds Need Light to Germinate and Others Don’t

Understanding which seeds need light to germinate can be the key to a successful garden! We have a simple trick to tell them apart.

Seeds are incredibly smart, evolving and adapting over thousands of years so they sprout at the perfect time. They can tell the difference between light and dark, and even between the sun’s intensity during spring or winter. In general, there is a theory that flower seeds need light to germinate, while vegetable seeds germinate in the dark. Let’s look closer to the reasons why this theory exists and whether or not it is true.

Some seeds need light to germinate because light serves as a signal that they are near the soil surface, where conditions are favorable for growth. These seeds are usually very small and lack the energy reserves to push through heavy soil, so trying to germinate in darkness deep underground would lead to failure. In general, most flower seeds fall into this first category. Light triggers specific photoreceptors in these seeds, activating enzymes that start the growth process. 

On the other hand, larger seeds with stored nutrients, like most vegetable seeds, do not require light because they have the resources to emerge from deeper soil. These seeds don’t need light signals because they rely on moisture, oxygen, and warmth to kickstart germination. Light becomes important only after the seedling emerges, when photosynthesis begins.

This difference is an evolutionary adaptation that ensures each type of seed germinates in conditions best suited to its survival.

Most gardeners follow the rule that tiny seeds need light to sprout, so therefore you shouldn’t cover most flower seeds, while bigger seeds have enough energy to push up through the soil, therefore vegetables can be sown deeper. But as with everything in nature, there are some fun exceptions. For example, even though Johnny jump up and corkscrew vine are flowers, they produce larger seeds and therefore germinate in the dark. On the flip side, lettuce and celery are vegetables, and while most vegetables germinate in the dark, these seeds are small and need light to germinate.  So, the theory that flower seeds need light to germinate and vegetable seeds need dark to germinate is a general theory, so don’t hold us to it 100%! But, you can rely on it when you need to make a decision and your hands are too dirty to look up the info on your phone. One way to always be right is to check the back of the packet or refer to our planting guides prior to starting your seeds. 

Happy germinating!