Do Seeds Need Light To Germinate? (Which Ones Do?)


Seeds are tough and can handle a lot of abuse, but they do need certain conditions for germination to occur.  For example, each seed needs the proper soil temperature and moisture to germinate – 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, and a general rule is that they should be covered with soil twice as deep as their diameter.

Of course, 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 to get the right amount of light or darkness for your seeds to germinate.

Let’s shed some light on this topic.

Do Seeds Need Light To Germinate?

Some seeds do need light to germinate, and some need only a thin layer of soil to cover them.  However, most seeds can germinate in darkness or light.

According to the University of Maryland Extension, for seeds that do not need light to germinate:

“A suitable planting depth is usually about twice the diameter of the seed.”

https://extension.umd.edu/hgic/topics/starting-seeds-indoors

For example, if a seed is ½ inch in diameter, you should cover it with 1 inch of soil.  According to the University of Maryland Extension, you can plant seeds deeper in sandy soil and shallower in clay soil.

winter melon seeds
A guideline is to plant seeds at a soil depth of twice their diameter.

What Happens If You Plant Seeds Too Deep?

If seeds are planted too deep, they may fail to germinate.  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).

tomtao seedlings
Seedlings may never germinate or emerge from the soil if they are planted too deep.

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 can wash away the soil covering the seeds and eventually the seeds themselves.  It is also easier for wildlife to find shallow seeds by digging in the soil.

cardinal
Birds are more likely to grab seeds that are buried too shallow (or not buried at all!)

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:

  • 1. Seeds that need light to germinate (they should not be covered by soil)
  • 2. Seeds that need thin covering to germinate (you should cover them with a thin layer of soil)
  • 3. 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, here 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
green lettuce
Lettuce seeds need light to germinate.

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.

This grow light system from Gardener’s Supply Company includes a rack to hold seed trays and adjustable lights that can be raised as plants grow.

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
onion seedling sprouts
Onion seeds need a thin layer of soil to germinate.

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
green shoulders on tomato
Tomato seeds can germinate in total darkness.

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 in tomato
Tomato seeds to not need light to germinate.

Tomato seeds should take 6 to 11 days to germinate under ideal conditions.  If you are having trouble getting tomato seeds to germinate, check out my article here.

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
Pepper seeds do not need light to germinate.

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 my article here.

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).

bolted lettuce
Lettuce seeds do need light to germinate.

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 here.

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
Basil seeds do not need light to germinate.

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 a thin layer of soil to cover them.

onions
Onion seeds do not need light to germinate, but they prefer a thin layer of soil covering them.

According to the University of California Extension, the ideal soil temperature for onion seed germination is 65 to 85 degrees Fahrenheit (18 to 29 degrees Celsius).

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.

According to Johnny’s Selected Seeds, the ideal soil temperature for coriander seed germination is 75 degrees Fahrenheit (24 degrees Celsius).

coriander seeds
Coriander seeds do not need light to germinate. The leaves and stems of the plant are also known as cilantro.

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.

According to the Iowa State University Extension, the ideal temperature for Zinnia seed germination is 70 degrees Fahrenheit (21 degrees Celsius).

zinnia
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 seedling
Cucumber seeds do not need light to germinate.

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.  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 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 learn more about what seeds need to germinate in my article here.

Finally, remember that all seedlings need light after the seeds germinate.

I hope you found this article helpful.  If so, please share it with someone who can use the information.

If you want to read some of my most popular posts, check out the “Best of GreenUpSide” page here.  Enjoy!

~Jonathon

jonathon.david.madore

Hi, I'm Jon. Let's solve your gardening problems, spend more time growing, and get the best harvest every year!

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