Lighting for seedlings can be a complicated topic, but it doesn’t have to be. In this post, I will break it all down, tell you everything you need to know, and give you tons of details about how and when to put light on germinated seeds.
Most homes don’t have enough natural lighting for seedlings, and trying to grow them on a sunny windowsill will only result in disappointment and wasted time (and money!).
Adequate lighting is a key part of successful seedling care, and it will give them a good start to life. When they don’t get enough, seedlings become weak and leggy, and may not survive for very long.
This is one of the biggest frustrations for new gardeners, but it’s a common problem that’s easily fixable. The only way to prevent leggy seedlings is to use grow lights.
Don’t be intimidated, I’m going to make this super easy for you in this detailed guide!
Below I will walk you through all that you need to know so you can get it right every time.
Table of Contents
Why Use Artificial Light For Seedlings?
The first few years I tried growing plants from seed, I didn’t use any artificial lighting for them.
I’m lucky enough to have a nice large south facing window in my spare bedroom, so I set up a few shelves right in front of it.
That worked ok, but my seedlings were always thin and weak looking compared to the ones I saw for sale at the garden center.
Things got worse for me once I started to experiment with different types of seeds. It quickly became clear that my sunny windowsill wasn’t going to provide enough light for all of them.
In those early years, my homegrown starts were always weak and spindly. Many of them would just get really tall and skinny, and then eventually flop over.
I discovered the hard way that they never recover from this, and the plants don’t do well in the garden either. I realized I was wasting a lot of time and money (and heartache) just to save a few bucks on artificial lights.
That’s when I decided it was time to buy myself some seedling grow lights, and I was amazed at what a difference it made!
Not only did my seedlings look fantastic, but adding a few artificial lights meant I didn’t need to plant as many seeds.
That’s because my starts were much healthier and stronger, and had no problem surviving the transition to the garden.
Do Seedlings Really Need A Grow Light?
In order to grow strong, healthy seedlings, it’s super important to provide the proper lighting for them right from the start.
That being said, you don’t absolutely need indoor seed starting lights if you have a sunny windowsill, porch, or another space filled with natural sunlight.
I’ve started lots of different types of seedlings in my sunny spare bedroom, and they survived just fine (though they were always a little leggy).
But if you ask me if the expense of buying grow lights is worth it – I’d say yes, absolutely!
So, if you’re a beginner and you don’t want to invest a ton of money up front, then go ahead and try keeping your seedlings in a sunny window.
It never hurts to experiment to see what works best for you, and in your home. Just make sure it’s south facing, and the trays are as close to the window as possible.
Once you have a few flats going, and you know you’re in it for the long haul, I would definitely recommend investing in proper lighting for seedlings.
Benefits Of Putting Seedlings Under Lights
There are tons of benefits to using the proper lighting for seedlings. Below I’ve listed the main ones, so you can see why it’s so important.
- Stronger and healthier seedlings – The main benefit of using artificial lights is that your seedlings will be much stronger, healthier, and stay more compact than they would just sitting near a sunny window.
- Better survival rate – Once you provide enough light, you’ll find that the survival rate of your seedlings is much higher. So you won’t have to plant extras to make up for all the weak ones you would have ended up losing.
- Less waste – Since you won’t have to plant extras to make up for those losses, there will be much less waste. You won’t waste any seeds or dirt… or your time. Because of this, you’ll find the lights will pay for themselves pretty quickly.
- Much easier – Providing proper lighting for seedlings will make your life so much easier too. By using a timer, you can just set it and forget it, rather than having to constantly monitor and rotate your trays.
- Prevents legginess – The only way to prevent seedlings from getting tall and leggy is to provide adequate lighting.
- Grow seeds anywhere in your house – Another benefit is that you can put your seedlings anywhere in the house. You don’t need to worry about keeping them in a room that gets tons of natural light.
What Kind Of Light Do Seedlings Need?
I mean… lights are lights, right? Nope! But you probably already knew it couldn’t be that easy.
It’s very important to make sure you get the right type of lighting for seedlings, and all bulbs are NOT created equal.
Just go to the hardware store, and you’ll see that now more than ever there are tons of different types of light bulbs to choose from.
Don’t worry, I’m not going to get super technical on you here, I want to make this very easy!
But it is important to understand that some bulbs (like regular incandescents) are way too hot, and will only end up frying your seedlings.
So what kind should you buy then? That’s easy! Your first option is to buy ones that are specifically made for this purpose – and those are called plant grow bulbs.
You can find them for sale just about anywhere these days, and simply put them into a lamp of your choice. They come in standard sizes that are made to fit into any light fixture.
Another great option is to use standard cool-white fluorescent bulbs. I made my own seedling grow lights using a standard shop fixture and fluorescent light bulbs. Get the step by step instructions here.
If you don’t want to mess around with assembling your own, or you’re not sure how or where to hang it, then I recommend getting a full system like this 4′ LED grow lights set up. Or something smaller like this one that’s 2′ long.
Another great option is T5 grow lights. Here’s a 2′ long one that I recommend, otherwise that same one also comes in an 18″ length if you need something longer.
How Much Light Do Seedlings Need?
Understanding how much light seedlings need is just as important as choosing the right bulbs. So in this section, I’ll tell you exactly how many hours they need, and give you examples of the best schedule to keep them on.
How Many Hours Of Lighting Do Seedlings Need?
Seedlings need 14-16 hours of light every single day, without fail. Don’t leave them on for 24 hours a day though. Like us, they need to rest at night.
So plan to keep your artificial lights on for 14-16 hours during the daytime, and turn them off overnight.
Use an outlet timer to make sticking to this schedule a snap, and ensure your seedlings get the perfect amount of light.
If you give them less than 14 hours of light per day, then make sure to monitor them closely. If they start getting tall or growing sideways, then give them another hour or two of light.
Best Light Schedule For Seedlings
Some people like to follow a 12/12 lighting cycle for their seedlings. That means the lights stay on for 12 hours a day, and they are off for 12 hours at night.
But in my experience, 12 hours is not long enough to keep all types from getting leggy. So I recommend leaving them on longer than that.
For example, I set my timer to turn the lights on at 6:00 am every morning, and turn them off at 10:00 pm each night. Keeping a consistent schedule like this is important for uniform plant growth.
If for some reason that doesn’t work for you, you could do a 7 am – 9 pm schedule, or use other similar times that work best for you.
The exact times don’t matter so much, but you should keep the schedule the same every day. And be sure to mimic the normal sun pattern by having them on during the day, and off at night.
How To Use Grow Lights For Seedlings
Learning exactly how to use grow lights for seedlings takes a little bit of practice. So below I will give you tips for when to start and stop using them, and how far away from the seedlings to hang them.
When Do I Put My Seedlings Under Light?
The answer to this one is simple. Your grow lights should be turned on (or your seedlings should be put under lights) as soon as the first seed starts to sprout.
Many types of seedlings grow very fast, and they will begin reaching for the light as soon as they emerge. So give them plenty of it right from the start.
How Far Should Seedlings Be From A Grow Light?
The grow light should not be very far from the seedlings. It’s best to keep it 2-3″ above the top of the leaves at all times.
So at first, your fixture will hang directly above (but never touching!) the plastic lid on the tray.
Once your starts get taller, and you take the lid off, then you’ll need to adjust the lights on a regular basis so they are always right over the top.
The leaves should never touch the bulbs though, or they could burn. So make sure to check on them every day, and move the light up as necessary. Using an adjustable hanger will make this job a whole lot easier!
Rotate the trays daily if you notice any of the seedlings around the edges are reaching, or aren’t growing as well as the ones that are directly under the light.
When To Stop Using Lights On Seedlings
The only time you should stop using lights on your seedlings is when they are outside. As long as they are inside the house, they should be under the lights.
Once you’re in the process of hardening them, you can turn off the lights while your seedlings are outside during the day. But, you shouldn’t stop using them completely until after you’ve moved the seedlings outside for good.
Just make sure you always put them under the lights each time you bring them back indoors, or they will quickly start to get leggy.
FAQs About Lighting For Seedlings
I’ve talked a lot about lighting for seedlings in this article so far, but you may have a few other questions. So now I’ll answer the ones I get asked the most. Post your question in the comments below if it isn’t answered here.
Do seedlings need 24 hour lighting?
No, and you should not put seedlings under grow lights for 24 hours a day. Just like us, they need to rest at night.
It’s important to follow a normal sunlight pattern, or your seedlings will suffer when it’s time to move them outside. So keep the lights on for 14-16 hours during the day, and turn them off at night.
Should you rotate seedlings under the lights?
If you provide the proper lighting for seedlings, then you should not need to rotate them. However, many times the trays are wider than the lamp.
So, you may notice some of the ones around the outside edges will start reaching. In that case, it’s best to rotate them daily to ensure even growth.
Can you start seeds indoors without grow lights?
Yes, you certainly could try starting your seeds indoors without grow lights if you have a sunny window for them.
However, most homes do not get enough natural light for healthy seedling development. So, for the best results, I recommend supplementing with artificial lights.
Do germinating seeds need light?
Whether germinating seeds need light or not depends on the type of seed. Some need light in order to germinate, while others do not. Always check the packet for details, or research the specific varieties before planting them.
Adequate lighting is extremely important for success with seedlings, and it will give them a healthy start to life. Plus you’ll find that it makes your job much easier, with less waste and frustration.
If you’re new to starting seeds, and you want to learn everything you need know in order grow your garden from seed, then you should enroll in my Online Seed Starting Course. This self-paced course will walk you through it all, step by step. Enroll and get started right now!
Otherwise, if you just need a refresher, or you want a quick-start guide, then my Starting Seeds Indoors eBook is just what you need.
More Posts About Seedlings
Share your tips about using artificial lighting for seedlings in the comments below.
DAVID DODD says
In south Florida we start our seedling in pots in late summer and leave them outside. My question is will I need to supliment the natural outdoor light since daylight hours are only about 10 each day.
Amy Andrychowicz says
You shouldn’t need to supplement the lighting for your seedlings outdoors, the sunlight is definitely much stronger outside than it is inside the house.
Vicki Ramsay says
I’m curious what you think about regular fluorescent lights that are found in typical school/office buildings. Last year was the first year I relied on these lights for my seedlings and they just seemed tiny, delicate, and a bit anemic compared to those I had grown in a greenhouse. Many of them didn’t thrive in the garden, although some did. This year, I bought two grow lights, but if I want to have all my seedlings under proper lights, I will need to buy more. Could I just buy replacement bulbs for the light fixtures? They would be very high then, and not adjustable, and would maybe get leggy anyway. Any advice would be appreciated! Thanks!
Amy Andrychowicz says
It is best to use plant grow light bulbs rather than regular fluorescent lights for your seedlings. However, regular fluorescent lights can work. The most important part is to make sure the lights hang directly above the seedlings (as close as possible without touching the leaves), and you keep them turned on for 14-16 hours every single day. If your grow light fixtures aren’t adjustable, then you can either buy an adjustable hanger (which I link to in the article), or try making your own custom stand (you can modify my design to fit your needs).
Sam says
First year germinating from seed. I started my seedlings about 4 weeks ago, and only now noticed my timer hasn’t been working. So my vegetable plants have been getting 24/7 grow light since they were first planted. I’m seeing all over that 24/7 light is not good for the plants and that they need a rest cycle. Am I able to save them by giving them a proper light cycle for the last few weeks until I harden them for transplanting outside?
Or will they just not survive because of too much growth?
Amy Andrychowicz says
No worries, just set the timer to the proper light cycle, and the seedlings should adjust fine.
Rusty says
Thanks for all the Great information.
So I am using LED grow lights to start my seedlings. Some shelf racks have one light and some two. Which seedlings would benefit from being on the higher lighted shelves ?
Thank you for your time and assistance !
Amy Andrychowicz says
The seedlings that grow the fastest would benefit from being on the higher lighted shelves. If any of the ones getting lower light start to become too tall or are reaching for the light, then move those up. Check on them daily and rotate as necessary.
Tyler Wachna says
We started our seedlings inside a little earlier this year, and they are thriving, but we don’t plan to plant outside for another 1-1.5 months and they are out of space in the greenhouse shelves we are using. I was thinking of moving to larger shelves, but then we will lose the greenhouse covers that keep their growing space warm and moist… Any tips? Tomatoes and Peppers, now 8-12″ tall…
Amy Andrychowicz says
I would start hardening them off to get them ready to move outside. 1-1.5 months is the perfect amount of time to do that. Here’s how to harden your seedlings.
Warren Shore says
Do you know how to bypass the timer on the grow lights? My grow lights only go to 12 hours and I want to use a mechanical timer to get 16 hours of light
TIA…Warren Shore
Amy Andrychowicz says
Sorry but I’m not sure how you could by pass the built in timer on your lights. You might either need to get a different type of grow lights, or just manually turn them back once the 12 hour timer runs out.
Steve Stansbury says
Amy, we live in the mountains near Boone, NC at about 3800′. It can get pretty cool in April. Do you recommend using one of those heating pads underneath the containers along with a light? We’re hoping to start perennials. We are also starting some dahlia tubers at the same time. Thanks.
Amy Andrychowicz says
Yes, adding bottom heat will help to increase the success rate and speed up germination. Good luck with starting your seeds!
Heidi Nagy says
What I am confused about is the concept of blue, red, and clear light. I have noticed that you used clear/bright light bulbs.
Amy Andrychowicz says
To make it easy, just look for either a plant grow light bulb or a “full spectrum” one (which will include both red and blue light, both of which are important for plant/seedling growth).
Naomi says
What if you are growing seedlings for a partly shaded area? Would you still provide full light for the 16 hours? And then slowly wean it down once they are strong enough…?
Amy Andrychowicz says
Yes because the natural sunlight outside, even in the partial shade, is much stronger than it is indoors. Having the lights on your seedlings will ensure they grow strong and healthy, and don’t get tall and spindly. And, even though the seedlings are for partial shade, you’ll still need to harden them off when you move them outdoors, to prevent sunburn.
Cecelia says
What kind of soil do you use? I planted salad almost 2 months ago and my seedlings are not even 1/2” tall. My ph is good and seeds to because it’s the same with the mache.
Amy Andrychowicz says
I usually make my own, here’s the article with my recipe and tips for the best type of soil to use. The fact that your seedlings aren’t growing could be caused by a few things, including lack of light, heat, water…etc. This post will help you troubleshoot and figure out how to fix the problem.
Cindy Kruger says
Thanks fo the great information. Do you know the difference between the two light colours on my grow light. There are 2 switches, one red and one blue. Do I turn both on for seedlings?
Amy Andrychowicz says
Sorry, but I’m not familiar with those switches. If you no longer have the box, then I would look up your specific type of seedling grow lights to see if you can find instructions online.
Clayton Pearson says
Hi Cindy,
The blue lights are for the lower end of the spectrum (the seed starting and growth stages). The red lights are for the upper end of the spectrum (the bloom and fruiting stages). In my experience, if you use both on seedlings you may get really dark green plants, but they may develop more slowly.