Guide: How to Start Seeds Indoors

Growing your own garden is an easy and cost-effective way to enjoy organic herbs, fruits, and veggies right at home. But instead of just winging it, you’ll want to make sure to follow the proper steps to garden success—including starting your seeds indoors, instead of directly in outdoor soil.

So what is the best way to start seed indoors? Take this dive into Tiffany Selvey’s Frugal Indoor Seed Starting course with us and get a quick tutorial on all of the basics that you need to know about how to start seeds and care for them until they’re ready to be transferred outside.

How to Start Seeds Indoors—and Why You Should

Seeds need just the right environment in order to sprout into plants, and providing this optimal environment is a big part of your job as a gardener (if not your entire job).

Where things get tricky is that you don’t have control over what sorts of elements your seeds might come into contact with once you plant them outdoors. And for plants that have a long growing season—for example tomatoes, peppers, onions, and eggplants—starting the germination process inside gives your seeds a controlled environment in which to sprout, regardless of non-ideal outdoor temperatures and conditions.

Figuring out how to start tomato seeds indoors, or any seeds for that matter, is all about technique and timing. Because cold weather can be deadly to young plants, you don’t want your plants to go outside until after the last frost of the season has occurred. In general, this means that you’ll get your seeds planted indoors about six to eight weeks prior to the final frost so that they’ve already made plenty of progress by the time you move them outside.

As for the seed starting process itself, here’s where we’ll turn to Selvey’s course, since she outlines all of the steps you’ll need to take to go from seed to sprout indoors. For even more in-depth instructions, we recommend watching her full course, which you can then follow up with other helpful classes like Geraldine Levin’s Gardening 101: A Guide for Growing & Caring for Plants.  

Indoor Seed Starting in 3 Simple Steps

How do you germinate seeds? It all starts with a plan, including figuring out what you want to plant, what you need to get started, and how to proceed with the actual planting process. And fortunately, we’ve got the steps you need to get growing right here.

Step 1: Collect Your Supplies

There are both optional and non-optional supplies that you’ll need to get your seeds going indoors. Here’s an overview of what you’ll want to have on hand, including what you can skip out on.

Shelving

You’ll need a sturdy seed starting shelf for your plants to rest on. To accommodate shop lights (more on those next), plan for your shelf to be about four feet wide. Many indoor gardeners opt for metal or plastic shelving, but you can also make a simple seed shelf out of wood.

Grow Lights

Once your seeds sprout into seedlings, they’ll require just the right amount of light in order to grow productively. Artificial grow lights help you provide this, with a couple options depending on budget. LED lights are the priciest option, but unless you’re planning to grow plants to maturity inside then you can probably go with basic shop lights instead, which should run you around $15. You can hang these above your shelf with an adjustable chain with S-hooks.  

Heat Mat

A heat mat is a specialty heating pad that goes under your seed containers to warm the soil for proper germination. At about $20 each they’re not super expensive, however they’re also not totally necessary so long as you’re able to keep your home at a consistent 60 degrees Fahrenheit or warmer.

Seed Containers

You have tons of options when it comes to what you plant your seeds in. One of the cheapest and most effective is newspaper pots, which you can learn how to make here. Plastic cups, egg cartons, or old takeout containers work too. If using plastic, poke some holes in the bottom to allow for drainage. And because your seed containers will need to drain, get a dishpan or aluminum pan that you can place them in on the shelf.

Selvey warns against using the types of unconventional seed starting containers you might have seen trending on Instagram or TikTok—think lemon rinds, eggshells, and ice cream cones. All of these are prone to rot and mold over the eight weeks or so that they’re in your home, which in addition to being pretty gross when you go to transplant, also isn’t so conducive to growing healthy organic plants.

Seed Starting Mix

There are three primary elements you need for how to start plants from seeds: heat and light, which we’ve already covered, and seed starting mix—a.k.a. soil.

You can make your own seed starting mix by combining two parts top soil with two parts compost and one part vermiculite. You can also purchase it pre-made at the store.

Step 2: Plant Your Seeds

Now comes the fun part!

Place your seed containers in your dishpan or aluminum tray. From there, fill each container with your homemade seed starting mix.

Look on your seed packet for directions on how far down each seed needs to be planted in the soil. If there isn’t any guidance, or just as a good rule of thumb, Selvey says to plant the seeds twice as deep as their diameter. Add two to three seeds to each container, since there’s a chance that not all of your seeds will sprout.

When your seeds are snug in their containers, cover with a loose layer of soil and use a spray bottle to add some water until the soil is damp (but not soggy). Make sure to label each container so you know exactly what’s sprouting where.

Step 3: Care for Your Seedlings

Your seed starter mix has everything your seeds need to germinate, so don’t worry about fertilizing just yet. Instead, continue to spritz your seed containers whenever the soil is dry to the touch—again, aiming for the soil to be damp and not soggy.

As your seedlings start to emerge, make sure to give them plenty of time under your grow lights and to maintain a warm enough temperature, using a heating pad if necessary depending on the temperature in your home. After a few leaves have sprouted, start to apply an organic fertilizer weekly. When your seedlings are mature enough and the last frost of the season has come and gone, you can go ahead and plant them outside.

Once you know how to start seeds, you’re halfway to being a pro at growing your own edible garden right at home. Expand your repertoire—and your pantry—by growing herbs in containers, as well as sprouts and microgreens. 

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