Seed starting 101 & how I start my seeds indoors (2024)

Do you want to start gardening and seed starting but don’t know what you need? In this seed starting 101 post, I share how I start my seeds and what works for me.

Seed starting 101 & how I start my seeds indoors

Hey everyone! Today’s post really gets back to basics, because I’m walking you through how I start my seeds indoors. If you’re wanting to start gardening and starting some seeds, you might be a bit intimidated. I know I was.

In this post, I’m going to walk you though how I start my seeds indoors. Keep in mind that there are TONS of different ways to start seeds indoors. This is what works for me, and you can choose to take parts of it and leave the others 🙂

I’ll also touch on a few important questions to ask yourself, like whether you should even start seeds to begin with or if it makes more sense to buy small plants to transplant into your garden.

I’ll also talk about the absolute necessities and things that are just nice to have. Seed starting (and gardening in general) can get pretty expensive if you aren’t careful. So let’s get started!

Supplies I use to start seeds:

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• Brick of seed-starting mix
• Bucket & water
• Something to grow the seeds in like these
• Fox Farms Grow Big or other fertilizer
• Grow lights (can be optional)
• Heat mat for germination (can be optional)

And here’s my seed starting 101 guide!

• My seed starting 101 guide
  • Step 2: Prepare seed-starting mix
  • Coconut coir vs. peat moss
• Do I need to use a heat mat to start seeds?
• Do I need to invest in grow lights to start seeds?
• When do I need to thin out my seeds?
• How do I know when to pot up my seedlings?
• How do I harden off my seeds?
• Do I really need to start seeds?

Step 1: Determine timing & when to start

When you plant seeds depends on a lot of things—namely the climate where you live and the type of plants you’re growing. To organize everything, I created a quick spreadsheet that had weekly columns.

I based these columns around our last frost date, which you can find by putting your address into the USDA’s plant hardiness map. I’m zone 7a, so my last frost date is mid-April.

I then had a row for each seed I was started and marked when I would start it indoors, when I would transplant it outdoors, and when I’d start direct sowing the seeds outdoors (once it’s warm enough). This can be as simple as a list, but I love throwing together spreadsheets to wrap my head around things.

I saved a lot of seeds from last year (mostly zinnia seeds), but I also ordered some seeds to save. Here’s what I will be starting indoors this year:

• Lettuce and spinach—these aren’t typically plants you’d start indoors because the root systems are fragile. And I’ve always direct-sown mine. However, I want to try starting them indoors to germinate them and then transitioning them outdoors to see if I can get another crop in.
• Kale
• Spoon tomatoes
• Peppers—I wasn’t planning on these, but I got a free seed packet!
• At least 5 different varieties of zinnias, dahlias, gomphrena, daisies—all for my cut flower garden
• Moonflower vine and clematis seeds I saved from last year
• Sunflower seeds

Step 2: Prepare seed-starting mix

The next step is to prepare your seed-starting mix. Seed-starting mix doesn’t actually contain any soil, unlike potting mix. The mix you use to start seeds is light and airy with excellent lightweight moisture retention.

You can buy a bag of seed-starting mix. You can also buy seed-starting setups that come with grow pods. Sometimes the grow pods will have fertilizer mixed in, sometimes they don’t.

But I went the budget route this year, using a brick of coco coir. I actually use coco coir for my houseplant mixed, too—so I went ahead and bought a two-pack online for about $13. I used only one of the bricks for my seed-starting mix—it makes a lot of mix!

Each of the bricks expands into 8 quarts of seed-starting mix. There are instructions on the packaging for how much water to add, but I just threw a brick in a bucket and added just under the recommended amount of water. I think it was 4.5 liters, and I added 4.

Coconut coir vs. peat moss

You might see “peat moss” referred to when talking about seed-starting mixes. Coco coir is a great alternative to peat moss. Peat moss is not a very renewable resource, and it’s super important that don’t use it all up.

Coconut coir is a great alternative. It is made from coconut husks and provides a light, sustainable growing medium that holds the perfect amount of moisture for starting seeds. It is 100% biodegradable, and I love how you can store the bricks until you’re ready to add water and use them.

Step 3: Prep & fill your containers

Much like there are a lot of options for seed-starting mixes, there are a lot of vehicles you can use to start your seeds. I like these little plastic containers because they hold up pretty well and can be used to several years.

I first started using these for plant propagations years ago—and also for starting succulents from seed. In my opinion, these are great because they take up much less space. Big seed-starting trays aren’t super practical for me.

Each of these small trays, however, has 12 different slots for growing. I can fit 6 of them on each tier of my greenhouse cabinet, so that’s a huge plus for me.

I would say that these are pretty hardy. You’ll need to do a deep clean of them at the end of seed-starting season, but you will definitely be able to use them again next year. As a bonus, you can use them for plant propagations after seed-starting season is over.

To get started, I just lightly pack the moist coco coir mix into each of the little sections of the planter. For some seeds, I filled up each section and then planted seeds with a toothpick. For others, I just filled the sections up halfway, added a seed, and then covered it.

As for number of seeds per pod—this depends. If I had a bunch of seeds, I did 2-3 per little section and will thin them out (basically pick them out and leave only one plant in there) when they sprout. If I didn’t have a lot of seeds (like the moonflower vine seeds I harvested), I just did one per section and am crossing my fingers.

Make sure you read the packaging for the seeds you’re starting to see if you need to soak them for 24-48 hours before planting. Also, you’ll want to take note of the recommended planting depth—though I mostly just throw the seeds in!

Step 4: Water & add nutrients

After I was finished planting all of my seeds, I took the trays over to the sink and watered them. The substrate was already a bit moist, but I wanted to add some nutrients. Coco coir doesn’t have any of those.

So I grabbed my container of Fox Farm Grow Big Liquid Plant Food. This stuff isn’t cheap, but guess what? It lasts FOREVER! You only need to use a tiiiiiiny bit in your watering can to get all of the benefits.

You can use it for seed starting, for fertilizing existing plants growing in your garden, and even for houseplants. So you’ll need to factor its longevity in when deciding if it’s worth the price. I expect it will last me the entire growing season and maybe even longer.

Step 5: Store in optimal conditions & monitor

I decided to put my seed-starting setup in my Ikea greenhouse cabinet. I chose this because it is out of the way and already has some bar grow lights and one seed-starting mat.

For the light—I keep them on for 9-12 hours a day because this area is not close to a window at all. And the room stays pretty warm—so while the heat mat isn’t totally necessary, I have it for plant propagations, so I’m going to use it!

Make sure that the coconut coir remains moist. You can fill the water reservoir and let the plants drink up the water they need. Or you can water the seedling from the top and keep just a bit of extra water in the bottom. That’s currently what I’m doing to get started.

If you keep the lid on, very little of the moisture will evaporate. Make sure you monitor them, though!

Do I need to use a heat mat to start seeds?

No, you do not need to use a seed-starting heat mat. They aren’t expensive if you want to get one for some of your plants that might germinate faster with a bit of extra heat. But in general, you’ll probably be fine without one.

Especially if the room you’re storing your seeds in is relatively warm. Ours is on the main level of our home, and we often run a little space heater in there as well. Sometimes my husband makes it feel like a sauna.

However, if you’re starting your seeds in a basem*nt, you may want to consider if a heat mat would be helpful. Our basem*nt stays very cold, so I would probably want to add one if I were starting everything down there.

Do I need to invest in grow lights to start seeds?

Whether or not you need to invest in grow lights to start seeds really depends on your setup. Do you have a home with a very sunny window? Is that room a suitable space for you to add your seed-starting planters to?

It’s possible that I could start my seeds in my sunroom. It gets very good light on sunny days. And it isn’t drafty, so I wouldn’t have to worry about the seeds getting too cold next to a window.

But you’ll want to keep in mind that multiple rainy or cloudy days might not be great for seed-starting germination. Some seeds might also perform better germinating in a windowsill, too—like zinnias. Super easy seeds to germinate. Tomato seeds, though, generally benefit from more warmth and light.

You may also choose to move your seedling trays outside on sunny days to help give them some more exposure. This really depends on your climate and temperature, but I’ve definitely heart of people doing it.

Grow lights do not have to be super intimidating and expensive. They are actually very affordable these days. You can read my post about grow lights and how to use them with houseplants for a few great options.

Many come with timers and intensity controls on them like the strip grow lights pictures below. Others you can simply screw right into a regular lamp.

When do I need to thin out my seeds?

Seeds don’t always germinate, so planting multiple seeds in a single growth area is a way to help guarantee that you get at least one plant per pod/section. You’ll need to thin them out if they all germinate, though.

As soon as the plants are tall enough to pluck them out, you can go ahead and do that. If you want to get crazy, you can try to pluck them out without disturbing the roots and pot them up separately. But I’m just going to chuck my extras since it’s pretty hard to transplant seedlings that small.

There’s one exception to thinning out that I am not going to abide by. I planted 2-3 lettuce and spinach seeds in each pod. I’m planning to start these indoors and move them outside to my GreenStalk planter in a few weeks once they germinate.

And I want to grow a few plants in each of the planter’s pockets to see how they perform. So I’m not going to thin those out. But when I sprinkle seeds in my raised garden bed, I will thin those out to ensure things don’t get too crowded.

How do I know when to pot up my seedlings?

It’s possible that you’ll need to “pot up” your seedlings—and this is a good sign! If your seedlings are growing well, you’ll notice that the roots will begin to poke out of your planter/growing tray’s drainage holes. Congrats—you’re killing it!

“Potting up” is basically just a fancy way of saying that you’re moving your seedling to a larger pot. You’ll want to do this if the temperatures aren’t high enough to move the plants outdoors. This will give them some more space to grow and develop while it’s still too cold.

When you do pot up your seedings, just move them to slightly larger containers. And you can switch over to a high-quality potting mix now. I love my Fox Farm raised bed soil—and you can also water the baby plants with some more of the Fox Farm Grow Big fertilizer.

Also try as hard as you can not to disturb the roots. Some plants are hardier than others when it comes to disturbing their roots. Lettuce grows very finicky roots, for example—so I won’t even bother potting my seedlings up. They’ll go straight into my GreenStalk planter.

How do I harden off my seeds?

Another topic you need to consider is “hardening off.” This basically just means that you’re acclimating your little baby plants to life outdoors. And it’s important—take it from someone who used to not know what hardening off meant and killed most of her seedlings one year 🙂

Are the temperatures are high enough to move whatever crop you’ve got outdoors (usually after your last frost date but can be earlier for cool-weather crops)? It’s time to start hardening your baby plants off.

And you can actually start this process before your last frost date if it’s warm enough during the day, which it probably will be! Here’s what I recommend doing:

• Start the process a few weeks before you plan on planting your crops outside
• Place your seeding trays in a shaded area on warm, dry days—take the lid off to expose them to the elements a bit more, and bring them in at night
• After a few weeks, your baby plants will have built up more of a tolerance to the different conditions they’ll experience in the garden—time to plant!

Do I really need to start seeds?

The last thing you should ask yourself is if you really want to start seeds in the first place. It’s definitely worth it if you want to grow a bunch of something—or even a few plants.

But it isn’t worth it for everything. I want to grow bush beans this year, but I only want to do one or two plants. So I’ll just opt to buy two plants at my local nursery and transplant them into my garden to save on the time and hassle.

For spinach, lettuce, and kale though? Growing them from seed is so easy—especially once spring hits! After spring hits, I direct sow everything straight in the garden. Starting seeds indoors in March is just a way of getting one extra crop in during the season.

Pin my seed starting 101 guide!