Starting seeds indoors is a great way to extend the growing season, but getting a head start on your garden indoors takes a little bit of knowledge. One of the trickiest things about it is learning when to put seedlings under light.
Table of Contents
- Why is Light Important?
- What Kind of Light is Best?
- When to Put Seedlings Under Light
- What is a Good Schedule for Grow Lights?
- How to Position Grow Lights
- When to Stop Using Grow Lights
- Final Thoughts
Why is Light Important?
Light is important for all plants, but seedlings need a lot of energy to grow. If you don’t give them enough light, they’ll get leggy and may not develop properly. If they survive, they may not last long when you transplant them into your garden.
What Kind of Light is Best?
The best lights for growing seedlings indoors are grow lights, either fluorescent or LED lights. Why? Because you have more control over them.
Growing seedlings indoors requires a certain type of environment. Ideally, in most cases, you need a setup with enough water and light. The temperature matters, too. By creating a space where you can control these things, your seedlings have a better chance at success.
You might be wondering why sunlight is not the preferred option. The truth is that, no matter how sunny a window you have, it’s likely not enough light for successful seedlings. Seedlings need at least 12 hours of sunlight to thrive, but 16 to 18 is better. You won’t be able to get this by relying on the sun.
When to Put Seedlings Under Light
Seedlings use light as energy to grow, so you should put seedlings under light as soon as you start to see sprouts coming out of the soil.
The first leaves you will see are called seed leaves, and they’re a little different from true leaves. Seed leaves are a part of the plant embryo, and their purpose is to use the energy reserves in the seed to encourage the plant to grow.
Once the first set of true leaves sprout, the seedling begins relying on photosynthesis.
Some seeds grow very fast, and seed leaves may give way to true leaves quickly. By having light available right away, the true leaves have an energy source from the moment they first appear, encouraging strong, healthy growth.
That said, it’s important not to keep seedlings under light for 24 hours a day. Seedlings need to rest, so give them at least eight hours with the grow lights turned off.
What is a Good Schedule for Grow Lights?
The exact time doesn’t matter, but you should stick to the same schedule every day. For example, if you’re aiming for 16 hours of sunlight for your seedlings and you’re an early riser, turn the grow lights on at 6 am and off at 10 pm, every day. Or, turn them on at 8 am every day and off at midnight.
You can surely start with closer to 14 hours and turn them on at 6 am and off at 8 pm or on at 8 am and off at 10 pm. But, if you notice your seedlings are getting long and leggy, you might need to increase to 16 hours a day.
How to Position Grow Lights
Knowing when to put seedlings under grow lights is only part of the puzzle. Knowing how to place seedlings under light matters, too.
Generally, the grow light should not be very far from the seedlings. Position them so they’re only two or three inches above the leaves at all times. This means that you have to continue adjusting the grow lights as the seedlings grow taller.
If the leaves are too far from the grow lights, they won’t be able to use the available energy effectively. If they’re too close, they can burn. Check your seedlings every day once you put them under light. They grow fast, and you don’t want to risk burning them.
Another thing to look for is if all of the seedlings are growing uniformly. For example, if the plants on the edges of the tray are reaching or getting leggy, you may need to start rotating them to even out exposure.
When to Stop Using Grow Lights
As long as your seedlings are indoors, you need to keep them under light since this is the only way they can photosynthesize.
When hardening seedlings to prepare them for life outside, make sure you put them back under the grow lights when you bring them back inside, making sure they still get eight hours of darkness to rest.
Here are some of the things people wonder about the most when growing seedlings indoors.
Can seedlings get too much light?
Yes. As we mentioned, seedlings need at least eight hours of darkness to rest. Without this, they become stressed, which is likely to affect their growth. Even if they seem fine spending 24 hours under grow lights, they will have a hard time when it’s time to transplant them as the sun doesn’t shine for 24 hours a day.
Do you have to rotate seedlings when they’re under grow lights?
Not necessarily. Depending on your setup and how many seedlings you have, each one may receive enough light. If you start to notice one side of the tray getting leggy, rotate them once a day to even things out.
Do you need grow lights to germinate seeds?
It depends on the seed. Some seeds need light to germinate while others need darkness. So, research the seeds you’re planting to determine what they need.
Remember, seedlings need to be under grow lights when the first sprout appears, but they may not need them before that happens. It’s a good idea to have your setup ready to go before you see sprouts, but don’t start your lighting schedule until the sprouts appear.
As you can see, grow lights are essential for healthy seedlings. Even in the brightest windows, the sun is unlikely to provide enough light to support the healthy growth and development of your sprouts.
As for when you should put your seedlings under light, you should be ready to go from the day you plant the seeds so you can turn the lights on as soon as you see the first sprouts.