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How Long Can Seedlings Go Without Light

It is common knowledge that plants need light to grow the way they are supposed to. Light helps plants produce chlorophyll, which is the green pigment in plants. Seedlings need light to grow, no matter what kind of plant you are trying to grow. However, timed light is essential because it shouldn’t be under light 24 hours a day. 

In general, it is recommended that seedlings go no more than 12 hours without light. A seedlings cycle should be 16-18 hours of light with 6-8 hours of dark. Pushing seedlings for a full 24 hours without lights may not do damage to more hardy plants, but it is a very risky move.

Finding the right light and the right amount of light time for seedlings can be tricky. If you are curious for further details about seedling lights, what kind of lights they need, and more, you’ve come to the right place.

Why Do Seedlings Need Lights?

Apart from the fact that seedlings may not even germinate or grow much at all, there are many different benefits to keeping your seedlings under a light. 


  • Seedlings will sprout if they have natural sunlight; however, having them under lights will help speed up the process since the lights also provide lots of warmth.

Stronger Plants

  • Seedlings that are not under lights will not grow the strength they need to keep up. They will become fragile and have a weak stem and root systems. 

Kick Starting the Photosynthesis Process

  • Without the photosynthesis process, plants would have no way to take their energy and turn it into food. Without light, there would be no photosynthesis process. 

What Will Happen If a Seedling Loses Light?

Many things could happen to seedlings that lose light or don’t have light at all. First of all, they may not even germinate, so you may never even get plants. If they do germinate under poor light conditions (which is unlikely), the plant will be weak and fragile.

You may notice the leaves never getting very green and the stem looking very dainty and thin. Say you end up transplanting this weak seedling into a pot outside; there, it will have sunlight, but it may not live the healthiest life because it didn’t grow up properly. The plant will always be very fragile, and the harvest will most likely be smaller than normal. 

What Kind Of Lights Are Best For Seedlings?

Having a greenhouse environment is your best option for 100% germination to start seedlings. No, this doesn’t mean you have to go out and build or buy a greenhouse. You could have something simple like a plastic cover over your seed trays that sit on your counter.

Of course, they would have to be under a light. Natural sunlight will work, but remember, seed starts need 16-18 hours of light. So if the sun isn’t providing that much light, you need to set something up. There are so many different grow lights and light bulbs that you can use. I recommend putting them on a timer for all of these types of lights, so you never forget to turn them on or off. Here are my favorites. 

T5 Lights 

  • T5 lights, in my opinion, are the easiest and best way to provide lights to seed starts. They are fluorescent lights. And they are small, 5/8 of an inch around, and in a long bar shape, so they are easy to set up. They usually come on or with a stand; they are easy just to put over the top of your seed trays. Typically, you will want to have your T5 lights 6 to 10 inches away from the tops of your seedlings. 

LED Grow Lights

  • LED lights emit a purple glow, resulting from red and blue bands of light that plants need to grow. LED lights are much more efficient than other lights, last longer, and are more environmentally safe. Because LED lights are stronger, they should be at least two feet away from your plants. 

Metal Halide Lights

  • Metal halide lights are trendy for seed starts. They have a very intense bright blue glow to them and produce light 3-5 times better than your average light bulb. They are also very warm, which means they also should be at least two feet away from your plants. 

What Seeds Do Better In the Dark?

Not all things in nature are the same. Everybody and everything is different, and some seeds can germinate in the light or the dark. These are some of the plants that can do both. 

  • Calendula
  • Basil
  • Eggplant
  • Peppers
  • Pumpkin
  • Zinnia 
  • Parsley

However, this only means they can germinate in the darkness. Once they have sprouted, all normal rules apply, and they will need the 16-18 hours of sunlight until they are ready to be planted outside. 

When Can Plants Go From Being Under Lights to Sunlight?

This is a process called “hardening” off your seedlings. There is a transition period needed for plants to get used to their new environment. The best way to put your plants in the sunlight in the morning then make sure they have shade in the afternoon and evening.

Bring your plants back inside at night. Do this for a few days; then, you can start leaving your plants in the sun, shade in the afternoon, and then the evening sun. Eventually, you will work your way up to sunlight all day. They only need to be brought inside for the first few nights. 

You will know your plants are ready to be hardened off once they have at least 3 or 4 leaves growing from the stem. They don’t have to be extremely tall, but 6 inches is ideal for taking them outside. 

Final Thoughts

Growing strong and sturdy plants from seed can be easy once you have trusty grow lights to put them under. They make a difference and ensure that your seeds are getting the right amount of light they need. Once you have the lights on timers, all you have to do is water them! It’s that easy! Happy gardening. 

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