Seedlings: How to Balance Grow Lights and Sunlight

It’s no secret that plants require plenty of light to grow strong. That’s certainly true for newly germinated (sprouted) seedlings, which need about 12 to 16 hours of light a day.

But, when it comes to light, it is possible to give your baby plants too much of a good thing. Seedlings need time in the dark, too, and excessive light can do more harm than good.

“When plants are getting too much light, it might show in the form of physical symptoms,” Fiene said. “You might see leaves drooping, discolored spots, or yellowing of the leaves.”

If seedlings aren’t getting enough light, they won’t produce as much chlorophyll, the green pigment in the leaves, Fiene continued, which can cause seedlings to turn yellow or white. Seedlings that need more light also tend to get leggy: long and thin-stemmed with few leaves. 

If you’re starting to worry that you won’t be able to give your seedlings the right amount of light, we have some good news. Achieving balance can be as simple as setting a timer. That’s what Fiene does.

“I have a timer set for my grow lights inside, and I set it for the longest time that's possible, 16 hours,” she said. “Then I don’t have to stress about the proper timing whether I get home late from work or I wake up late in the morning.”

Under the grow lights

During your seedlings’ first couple of months in your care, the grow lights you provide will be their source of indoor sunshine — sort of.

While sunlight contains a full spectrum of light, including all colors and wavelengths, grow lights usually emit specific wavelengths, usually in the red and blue spectrum, that are most conducive to plant growth. 

Plus, natural sunlight is usually more intense than artificial grow lights; its duration varies by time of day, weather, and geographic location; and sunlight shines down at varying angles as the sun moves across the sky. Grow lights allow you to control these variables and make sure your seedlings get the consistency and amount of light they need.

A huge variety of grow lights is available to you. Here are a few of your options.

Fluorescent: Fluorescent tubes are considered an affordable option. They emit a broad spectrum of light, suitable for various stages of plant growth, and they produce less heat than other types of grow lights, making it safe for you to place them fairly close to your seedlings. 

LED: These lights are known for energy efficiency, which could help you minimize your electricity costs. Because LED grow lights allow you to control their light spectrum, you can tailor them to your seedlings’ needs. These lights have a longer lifespan than other types of grow lights, but they also have higher upfront costs. 

High-Intensity Discharge (HID):  The lights emit high levels of light intensity, making them a good choice for large or tall seedlings. They also provide a broad spectrum of light, similar to natural sunlight, which can promote robust plant growth. On the other hand, HID lights generate quite a bit of heat and may require additional ventilation or cooling systems. They consume more energy than other options, too.

There is no “right answer” when it comes to selecting your grow lights.

“They all work; you just have to find one that works best for your budget and space,” Fiene said.

Keep an eye on your seedlings

When seedlings are ready to go under grow lights (after they’ve shot up above their planting material), pay close attention to the lights’ placement.

“Make sure your seedlings aren't touching the grow light, because that will cause obvious discoloration and burning,” Fiene said. “I like to place the light about three to five inches above my highest seedling. It may seem a little close, but my lights don't produce very much heat.”

No matter what kind of grow lights you use, you’ll want to monitor your seedlings closely for signs of damage or excessive heat. 

“If seedlings are turning brown, it can be a sign of too much light,” Fiene said. 

Adjusting to the sun

After about two months indoors, when you see roots coming outside of your seedling trays, it will be time for you to start hardening off your young plants. Put them outside during daylight hours for a couple of weeks before you transplant them into your garden. Not only will this process help your seedlings build defenses against the wind and temperature fluctuations, but it will also help them make the transition from grow lights to the intensity of the sun.

“I would put them in partial to full shade,” Fiene said. “I don't like to put them in the full sun, especially when it gets hot where we are here in Houston. It's going to really damage the plants and shock them.”

(Keep in mind, this transition period is for seedlings that started life indoors. If you sowed seeds directly into your garden, the seedlings shouldn’t have any problems handling the sunlight.)

When things start heating up

Generally, after you’ve transplanted your seedlings into your garden they should do fine with the sunlight.

One exception would be during intense summer heat, especially in regions of the country where temperatures soar above 100 degrees. In those cases, your plants could benefit from the protection of shade cloths.

You can now find seedlings and some of its accessories in the Vego Garden Seedling Suite.