Seeds are tough – they can handle a lot of abuse. Still, they do need certain things to germinate. For example, each seed needs the proper soil temperature and moisture to sprout – but what about light?
So, do seeds need light to germinate? Some seeds do need light to germinate (such as celery, dill, lettuce, and petunias). Other seeds prefer only a shallow layer of soil (such as onions and pansies). However, most seeds will germinate in darkness or light – a general rule is that they should be covered with soil twice as deep as their size.
You can see how soil temperature affects seed germination with this app I made!
After the seed germinates, all seedlings (sprouted seeds) need light to continue growing – this is not negotiable.
In this article, we’ll talk about which seeds need light to germinate and why. We’ll also talk about how deep to plant seeds to get the right amount of light or darkness for the best germination.
Let’s shed some light on this topic.
Hey – you can get our weekly gardening newsletter here!
Join 1000+ gardeners to get access to news, tips, and information.
Delivered right to your inbox – once per week.
Do Seeds Need Light To Germinate?
Some seeds do need light to germinate. Others only need a thin layer of soil to cover them. Most seeds can germinate in either darkness or light.
“Most seeds should be planted at a depth of about twice their diameter.”
https://extension.unh.edu/resource/starting-plants-seed-fact-sheet
For example, if a seed is ½ inch in diameter, you should cover it with 1 inch of soil. According to the Iowa State University, Extension you can sow deeper in sandy soil than in clay soil.
This is because loam and sand (made up of larger, coarse particles) dries out faster than clay (made up of smaller, fine particles).
What Happens If You Plant Seeds Too Deep?
If seeds are planted too deep, they will not sprout. This is especially true for seeds that need light to germinate or that need only a thin layer of soil to cover them (more on this later).
Deeper soil tends to be cooler, so planting too deep may deny seeds the warmth they need for germination. According to the University of California, most vegetable seeds germinate well at temperatures of 75 to 85 degrees Fahrenheit (24 to 29 degrees Celsius).
There is also less water at greater soil depths. This means that seeds planted too deep will lack the moisture they need to sprout.
Even if a seed germinates, it may never emerge above the soil if it is planted too deep. A newly sprouted seedling needs sunlight soon after germination (so it can begin producing energy through photosynthesis).
You can learn more about what happens when you plant seeds too deep in my article here.
What Happens If You Plant Seeds Too Shallow?
If seeds are planted too shallow, a hard rain or heavy watering will wash away the soil covering the seeds. Eventually, the seeds themselves will wash away.
It is also easier for wildlife to find shallow seeds by digging in the soil. Even if the seed does not fall victim to any of these problems, it may still fail to germinate.
If seeds are uncovered when rain washes soil away, they are totally exposed to birds, squirrels, and other animals that may want to eat them.
Even if the seeds do germinate, their roots may not develop properly. For example, according to the University of Nebraska at Lincoln:
“Corn roots may not develop properly when planting too shallow and the stands may not grow uniformly … The seed zone is also more likely to dry out when planting too shallow.”
https://cropwatch.unl.edu/avoid-planting-too-shallow
Which Seeds Need Light To Germinate?
When it comes to light requirements for germination, there are three main categories of seeds:
- Seeds that need light to germinate (they should not be covered by soil)
- Seeds that need thin covering to germinate (you should just barely cover them with, using only a thin layer of soil)
- Seeds that germinate in darkness or light (ideally you should bury them at a depth of twice the seed’s diameter)
The seed packet or catalog will often indicate light requirements. In case you lost track of this information, below are some lists of each type of seed.
Seeds That Need Light To Germinate
Some seeds need light to germinate. According to the University of Nebraska at Lincoln:
“The seeds do not need full or even partial sun, just daylight to induce germination.”
https://extension.unl.edu/statewide/fillmore/Seeds.pdf
These seeds should be pressed into the soil but left uncovered. Use a mister to keep the soil moist until germination occurs.
According to the Iowa State University Extension, the following seeds need light to germinate:
- Ageratum
- Alyssum
- Browalia
- Celery
- Coleus
- Dill
- Dusty Miller
- Impatiens
- Lettuce
- Lobelia
- Nicotiana
- Petunia
- Portulaca
- Salvia
- Scarlet sage
- Snapdragon
- Torenia
- Wax begonia
This list is not exhaustive, but it gives you a good idea of just how many seeds do need light to sprout.
If you are starting these seeds indoors, be sure to give them enough light to germinate. Placing your seed tray on a windowsill may be sufficient – but if the days are still short, you might need more light.
In that case, a grow light may be necessary to provide the light your seeds need. The University of New Hampshire Extension suggests that you can suspend fluorescent lights 6 to 12 inches above seeds for 18 hours per day.
Seeds That Need A Thin Layer Of Soil To Germinate
Other seeds need only a light covering of soil to germinate and should be left close to the soil surface. The following seeds should be covered only with a thin layer of soil:
- Dianthus
- New Guinea Impatiens
- Onion
- Pansy
Seeds That Can Germinate In Darkness
Finally, some seeds will germinate in darkness or light. According to the University of Missouri Extension:
“As a general rule, seeds other than especially fine seeds should be covered to a depth about two times their diameter.”
https://extension.missouri.edu/publications/g6570
The following seeds can germinate in light or darkness:
- Basil
- Broccoli
- Cabbage
- Cauliflower
- Celosia
- Cucumber
- Eggplant
- Geranium
- Kale
- Marigold
- Muskmelon
- Parsley
- Pepper
- Periwinkle
- Pumpkin
- Squash
- Tomato
- Watermelon
- Zinnia
Hey – want to take my FREE 1-week seed starting email mini-course?
Learn about starting plants from seed – in just a few minutes per day.
Sign up for the course and get started today!
Do Tomato Seeds Need Light To Germinate?
Tomato seeds do not need light to germinate. The ideal soil temperature for tomato seed germination is 65 to 85 degrees Fahrenheit (18 to 29 degrees Celsius).
Tomato seeds should take 6 to 11 days to germinate under ideal conditions (longer in hot or cold soil, or if the soil is too dry).
If you have trouble getting tomato seeds to germinate, check out this article to help solve the problem.
Do Pepper Seeds Need Light To Germinate?
Pepper seeds do not need light to germinate. The ideal soil temperature for pepper seed germination is 65 to 75 degrees Fahrenheit (18 to 24 degrees Celsius).
Pepper seeds should take 8 to 13 days to germinate under ideal conditions. If you are having trouble getting pepper seeds to germinate, check out this article for helpful hints.
Do Lettuce Seeds Need Light To Germinate?
Lettuce seeds do need light to germinate. The ideal soil temperature for lettuce seed germination is 60 to 75 degrees Fahrenheit (16 to 24 degrees Celsius).
Lettuce seeds should take 2 to 4 days to germinate under ideal conditions. If you are having trouble getting lettuce seeds to germinate, check out my article on lettuce seed germination.
Do Basil Seeds Need Light To Germinate?
Basil seeds do not need light to germinate. According to the University of Illinois Extension, the ideal soil temperature for basil seed germination is 70 degrees Fahrenheit (21 degrees Celsius).
Basil seeds should take 5 to 7 days to germinate under ideal conditions.
Do Onion Seeds Need Light To Germinate?
Onion seeds do not need light to germinate. However, they prefer only a thin layer of soil to cover them.
Onion seeds should take 3 to 7 days to germinate under ideal conditions.
Do Coriander Seeds Need Light To Germinate?
Coriander seeds do not need light to germinate.
Coriander seeds should take 7 to 10 days to germinate under ideal conditions.
Do Zinnia Seeds Need Light To Germinate?
Zinnia seeds do not need light to germinate.
Zinnia seeds should take 7 to 10 days to germinate under ideal conditions.
Do Cucumber Seeds Need Light To Germinate?
Cucumber seeds do not need light to germinate. The ideal soil temperature for cucumber seed germination is 65 to 95 degrees Fahrenheit (18 to 35 degrees Celsius).
Cucumber seeds should take 3 to 6 days to germinate under ideal conditions. If you are having trouble getting cucumber seeds to germinate, check out my article here.
Do Seeds Germinate Better In The Dark?
Many seeds germinate better in the dark. For example, tomato seeds germinate better in the dark.
In fact, according to Penn State University Extension:
“Most seeds germinate best under dark conditions and might even be inhibited by light. A few other seeds need light to germinate.”
https://extension.psu.edu/understanding-seeds-and-seedling-biology
Planting seeds in soil gives them darkness, but it also protects them from animal pests (birds, squirrels, etc.) that want to eat them.
The exception is seeds that need light to germinate, which we discussed earlier.
Conclusion
Now you know which seeds need light to germinate, which seeds prefer a light covering of soil, and which can germinate in darkness.
If you are having trouble germinating your seeds, remember that light may not be the problem. Temperature and soil moisture are other factors that play a role.
You can explore the possibilities for vegetable seeds and more here.
You can learn about direct sunlight for plants (and whether they need it) here.
You can find a full seed starting guide here.
You can learn more about what seeds need to germinate in my article here.
Finally, remember that all seedlings need light after the seeds germinate.
To find books, courses, seeds, gardening supplies, and more, check out The Shop at Greenupside!
Hey – you can get our weekly gardening newsletter here!
Join 1000+ gardeners to get access to news, tips, and information.
Delivered right to your inbox – once per week.
If you want to read some of my most popular posts, check out the “Best of GreenUpSide” page here. Enjoy!
~Jonathon