How to start seeds under grow lights indoors

How to Plant Seeds Under Grow Lights, A Step-By-Step Tutorial

You can get a head start in your garden in late winter or early spring by planting seeds inside under grow lights or near a window. It’s not too much work, and it’s really cost effective in the long run. A seed packet generally costs $1-$4 and contains anywhere from 10 to 300 seeds. Whereas most plants at a nursery start at $2 and can get very expensive as they grow bigger or are heirloom. You do need a grow light if you plan to plant indoors and you don’t have a room with great sunlight most of the day (I don’t, and my kids would make a huge mess with the dirt).

If you do plant indoors by windows, keep an eye on your seedlings to make sure they aren’t getting leggy (long and spindly) and leaning one direction.


The lights might be around $20, a stand is also $20. Or maybe you are crafty and thrifty and you can build your own stand and find a light on the cheap. I’ve had my light and stand for at least 5 years now and it’s definitely paid for itself.

The other great thing about growing from seed, is that there are so many more cultivars out there than are probably at your local nursery or hardware garden area. I went a little crazy on tomatoes this year, but look how fun these varieties are! Sorry about the shine from the t5 light ;). If you can’t see, I have:

  • Blue Beauty
  • Get Stuffed
  • Amish Paste
  • Kelogg’s Breakfast
  • Beefsteak
  • Mortgage Lifter
  • Raspberry Lyanna
  • Tomato Isis Candy Cherry
  • San Marzano Lungo No. 2
  • Sweeties
  • Romas
  • Plus Pink Brandywines I saved last year (not pictured)

Apparently the gardener that invented the Mortgage Lifter Tomato literally “lifted” his mortgage back in the 1930s buy selling each tomato for $1. He sold tomatoes for 6 years and was able to pay off his $6000 mortgage (source). Wouldn’t it be nice if mortgages were only $6000 these days (pretend inflation kept up with everything else)!

You probably just want to know how to plant seeds under lights (who cares how many seed packs this crazy tomato lady bought right?). On to it.

How to Plant Seeds Under Grow Lights

The following steps assume you already have a grow light. 

1. Set up your grow light. You want to put this in a place that’s not too cold as warmer weather seeds need warmer temperatures to germinate (at least room temperature). If you have a grow light stand like mine that lowers and raises, you are ready to go from here. If you don’t you will want to find a way to get your plants and light within inches of each other to start. As the seedlings grow, you will slowly raise the light to keep it just above the top of the plants. If your light is too high above the plants, they will become leggy and fall over. My seed magic happens in the furnace room. The floor is concrete, but it’s warm in the room with the furnace and a refrigerator nearby.

Another option to help the seeds germinate faster and more uniformly, is to use a heat mat. I haven’t used one myself, but it’s a nice add to the seed starting set up.

2. Decide on your growing medium and containers. There are a ton of mediums and containers that seeds can be grown in. If you want to do it the easy way, you can buy the jiffy type seed starting trays with the peat pods that go in each spot. You just add water and the pods expand out and up. There is some controversy on whether or not peat is a sustainable medium. So, if you are wanting to be eco-friendly, using a sterile seed starting mix might be the way to go. You can use left over multi-planters bought at a store previously, or make your own newspaper planters. I’ve tried using toilet paper tubes, egg cartons, and various plastic food containers. The important part is that you use a medium that is sterile (not potting soil). You don’t want a bunch of big sticks or gnat larva in your seed starting mix. If you use a sterile mix, fill the containers almost to the top, leaving about 1/4″ head space.

These little yogurt containers are perfect.

3. Plant your seeds. Make sure your growing medium is wet, but not soggy before you plant. If you squeeze the medium and it drips, it’s too wet.

You’ll want to come up with a system to remember which seeds you planted where. I like to make a diagram like this one:

And just label it as I go. Other people like to use plant label sticks or colored tooth picks. Do what works for you. But make sure you do label or you’ll most likely be smacking your forehead in two months from now.

I like to use the back of the pen I write with to push a little hole into each pod or planter and then drop 1-3 seeds inside. For most of my pods, I used 2 seeds. For seeds packs that I bought a few years prior, I added more seeds under the assumption that the viability of these seeds would be lower. If you have really expensive seeds like the Aji Charapita Pepper seeds that only have 10 in the whole pack ( $4.00), you might only want to put one seed in each hole since if two sprout, you do end up pinching one off. As far as depth, you’ll want to follow the instructions on the seed package. If there is no information, the general rule of thumb is double the seed width. So if it’s a tiny seed, plant it very close to the top of the soil. A large seed like a pea, plant it deeper.

After planting the seeds and covering them up, gently press down on the top of the soil to tamp the seed down. Then give each seed a light watering using a small container or spray bottle.

4. Cover the seed trays. While the seeds are germinating, you will need to put a cover over the seed containers. If you use a seed starting tray, it should come with a plastic cover. If not you could use another plastic top or even some plastic wrap to keep the seed trays evenly humid until the seedlings emerge. As soon as you see green, take the lids off.

Then lower your grow light to just above the seeds (or raise the seeds to just below the lights). Turn on your grow light and leave it on for 12-16 hours per day. A timer is at the plug is a great way to do this. Or you can, of course, manually turn the lights on and off each day. If you happen to forget to turn it on or off one or two times, the plants will survive. Just try not to make that a habit.

5. Fertilize your seedlings. After the true leaves appear (the first leaves that appear are called cotyledons, these are not the true leaves. The next leaves to appear are called “true leaves”), you can fertilize at 1/4 to 1/2 solution (as determined on instructions for fertilizer).

Now, how often, is up to you as well as which kind of fertilizer you use. Some sources say to fertilize twice a week, and other say once every two weeks. For many years, I didn’t fertilized at all. I do, however, think that fertilizing your starts is a good idea. The plants will be bigger, stronger, and healthier when it’s time to put them in the garden, which makes them less susceptible to pests and diseases.

The type of fertilizer is also a personal choice. If you want simple and cheap, buy a simple chemical liquid fertilizer like Miracle Grow. If you want to go more organic and sustainable, try a fish emulsion fertilizer (I guess they make ones that aren’t as stinky too!) or a seaweed based fertilizer.

6. Transplant to larger containers. Once the plants have outgrown the first container (unless you planted in larger containers to begin with), you will need to transplant them to something where their roots can grow out and not become bound up. If you look on the under side of the container and a bunch of long roots are dangling out, you know it needs something bigger.

7. Harden the plants off. Once the weather is warm enough to transplant your beautiful homegrown plants, you will need to harden them off. You might be saying, hard what? That’s just the term the gardening world uses to mean, get the plants used to being outside with wind and the strong sun and fluctuating temperatures. Your plants have been babied, it’s time for them to grow up and see the world. Anyway, bring the plants outside a few hours each day starting in a slightly shady area and moving up to full sun. You can do this in a matter of days or a week or so. Be careful, because the soil will dry out a lot faster outside especially if the containers are small.

Also, when you move the plants outside, be sure to mark the front of the container if you have diagrammed them so you know which seeds are which when you bring them back in.

8. Transplant your plants to the garden. After the plants have been sufficiently hardened off, you can put them in the garden. Don’t forget to check the frost date for your area if you are planting tender warm veggies like tomatoes and peppers.

That’s it! I hope I gave you enough information to get started. If you have any questions or comments, please let me know below.
Happy Gardening!
Spread Hobby Love!

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