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How To Start Seeds Indoors With Grow Lights: Ultimate Guide

Growing your plants indoors with grow lights can make all the difference. From choosing the ideal location to the perfect soil mix, and even down to the type of light you should use. This article will teach you the way to start seeds indoors with grow lights to give your seedlings healthy growth. 

How To Start Seeds Indoor Under Grow Lights? 

Here we will walk you through the steps to grow indoor seeds under a grow light. We will cover everything through 12 steps below: 

Step 1: Choosing the right spot for seed starting

Before you start planting, decide where you’ll set up and the type of light, some require sockets while fluorescent lights have to hang above your trays. Make sure to have seed trays for planting as well.

Tip: Seed trays are easy to use for beginners. The cells usually allow water in and roots to grow through. For a quick DIY option, you can use egg cartons with a small drainage hole at the bottom, or even empty toilet paper rolls.

Trays of vegetable seedlings under grow light 

Trays of vegetable seedlings under grow light 

Step 2: Preparing the soil

You loosen the soil mixture and make it slightly damp. Ensure there are no dry spots in this soil mix.

Step 3: Filling up the pots

Now, fill up your trays or pots with the soil mixture and then plant seeds over 2/3 of the surface area. After that, lightly tap the tray onto a table so the soil settles. Next, use your hand or a small board to lightly press down on the soil, avoiding compaction so it stays airy.

Step 4: Planting the seeds

You follow the instructions on the seed packet for specifics. Some seeds may need a period of cold stratification or soaking beforehand. Others may require a dark environment to germinate, while some need light to grow.

Step 5: Finishing up planting

Once the seeds are in, add some more damp soil on top and press lightly. Note that small seeds require less soil covering. Refer to your seed packet instructions for the correct amount of soil to add.

Tip: Even if your soil was pre-dampened, mist the top layer lightly. This will keep the soil moist and help with seed-to-soil contact.

Step 6: Label everything

To know which plant is growing where it’s essential to label each tray or pot. You can use popsicle sticks and markers to write the plant name and the planting date. Place these labels near the edge of the box or tray.

Step 7: Creating the environment

Now, you cover the trays with clear plastic to retain heat and moisture. Then, move the trays to a warm spot, away from drafts. The ideal temperature for most seeds is between 65 and 70°F. For added warmth, you could use special seed-heating mats under the trays but remember, this will require more frequent watering.

Step 8: Watching the seedlings grow

As soon as the seedlings start appearing, you remove the plastic cover and place the trays in indirect light (like under Grow lights). The seedlings will begin to develop two leaf-like structures called cotyledons.

Step 9: Set up grow light

Keep your light as close to the seedlings as possible without touching them (around 2 to 3 inches). When the seedlings emerge, you should keep the light on for 12 to 16 hours each day. To save time, you also use a timer to automatically turn the lights on and off.

The secret to robust seedlings isn’t just the duration of light they receive, but the quality of light. Investing in a good grow light is like giving your plants a head start in growing season.

Step 10: Keep seedlings moist

In this step, you must keep the seed-starting environment sterile and consistently moist but not wet. Moreover, remember to check the soil moisture at least once a day to ensure it’s not drying out. Additionally, maintaining the right moisture level also minimizes the risk of diseases like damping off by watering from below.

To water, you should place the seedling tray on a plate and pour a small amount of water into the plate for about 10 to 30 minutes. Then let the seedlings absorb water through the drainage holes or the foam material of the container. To check moisture, touch the soil surface with your finger. After checking, continue by moving the tray out of the plate and placing it back in its original position to receive light.

Step 11: Start feeding

As the seedlings grow and develop leaves, they will need food to continue growing. At this stage, you should use liquid plant food but dilute it to half-strength as stated on the package. The feeding frequency is once every two weeks.

Step 12: Give them a new place

At the growth stage, if the plants are too large for their small pots, move them to a larger pot. Now you can use regular potting soil. If multiple seedlings are in the same pot, remove the weaker ones.

Seeds growing indoors under fluorescent lights

Seeds growing indoors under fluorescent lights

Why Should I Seeds Under Grow Lights? 

Plants need special colors of light to grow well, especially red and blue light. Normal white lights don’t have these special colors. That’s why it’s good to use grow lights that have the full range of colors like the sun or just red and blue lights. This helps plants start strong.

You can find different shapes and kinds of grow lights. Some are LED lights that go in regular lamp sockets. Others hang from the roof or fit in special stands for seedlings. There are many old-style grow lights available today, but they use more power than modern LED or tube lights.

How Far Away Should Seedlings Be From A Grow Light?

You should keep seedlings 2-4 inches from soft lights like fluorescents, and 16-36 inches from strong lights like LEDs or HIDs. If you put them too close, they might get burnt. Besides, if you put them too far, they grow weak. Additionally, you also consider other things:

  • Plant type: Different plants need different light. Some, like tomatoes, need more and should be closer. Others, like herbs, need less and can be further away.
  • Light power: Brighter lights can be further from plants because they give off more heat and light. And weaker lights should be closer.
  • How you grow: If you’re using water-based growing (hydroponics), lights should be closer. For normal soil growing, they can be a bit further away.

Benefits of Growing Seedlings Under Grow Lights

First and foremost, the right grow lights for indoor plants ensure that they grow up to be strong and healthy. This increases their survival rate, meaning you don’t need to plant extra seeds to make up for any that didn’t make it. Therefore, you can save on seeds, soil, and the time it would take to replant.

Besides improving plant health and minimizing waste, grow lights also make the whole process more flexible for you. By using a timer to control the light cycles, freeing you from the chore of constant monitoring. Moreover, the use of grow lights means you’re not restricted to placing your seedlings in rooms with ample natural sunlight. Thus, you can place them anywhere in your home, giving you more freedom and flexibility in your gardening endeavors. 

Growing seedlings of tomatoes under LED light

Growing seedlings of tomatoes under LED light


Grow lights offer a variety of benefits for starting seeds indoors. They can help ensure that your seedlings grow up to be strong and healthy, increase their survival rate, and save you time and money. With this step-by-step guide, you’re well on your way to becoming an indoor gardening pro. 


How many lights do I need to start seeds?

For plants that love lots of suns, like vegetables, you’ll need around 2000 to 3000 lumens per square foot. If you’re just starting one standard seed tray, a single grow light with 3000 lumens will do the job.

Is it okay to keep the grow lights on for 24 hours for the young plants?

No, don’t keep the lights on for a full 24 hours. Your seedlings need around 14 to 16 hours of light each day, but they also need some darkness to rest. 

What sign to tell your seedlings are lacking light?

If your seedlings are stretching out and leaning towards the light, that’s a sign they need more light and you have to move the grow light closer to them.

Mike Rastus-Josiah

Mike Rastus-Josiah

Mike Rastus-Josiah is the Master Gardener of Swipe Garden. He has over 30 years of experience in horticulture, plant physiology, and sustainability practices. Mike wants to continue sharing his expertise with inspiring others to explore the wonders of gardening.