Exactly as the title says — this is an easy, no-fail guide to indoor seed starting.
You don’t need to read any gardening books first. You don’t need any fancy equipment. You just need your seeds (these are the best garden seed catalogs that I order from every year) and a few basic supplies to get started.
Whether you have a dedicated vegetable bed in your backyard, or a cluster of containers on your patio, it all starts out the same way. You have to plant your seeds, and germinating seeds inside your home (where you have the most control) is the best way to do so.
Starting seeds indoors is ideal if you want to get a head start on the season, or if the weather is still too hot or too cold to put anything in the ground.
- How to start seeds indoors: a step-by-step guide
- Step 1: Gather your seed starting supplies.
- Step 2: Fill your pots or trays with seed starting mix.
- Step 3: Sow your seeds.
- Step 4: Label your newly planted seeds.
- Step 5: Keep your seeds moist and warm.
- Step 6: Give your new seedlings light.
- Step 7: Moving day! Transplant the strongest seedlings when they’re ready.
- Step 8: Harden off those seedlings.
- Step 9: Transplant your seedlings outdoors.
- Where to buy indoor seed starting supplies
- What to know after your seeds germinate
This simple step-by-step tutorial will take you from seed to seedling with a minimum of fuss. Just the stuff you need to know, and none that you don’t. (But if you’re the really-need-to-know type, I’ve added footnotes at the end to explain why you’re doing what you’re doing.)
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How to start seeds indoors: a step-by-step guide
Step 1: Gather your seed starting supplies.
- Seed starting pots or cell trays
- Plant markers
- Seed starting mix (homemade or store-bought)
- Seed tray with humidity dome (often called a 1020 plant tray or propagation tray, or use any DIY drainage tray with plastic wrap)
- Spray bottle or squirt bottle filled with water
You can also repurpose household items into seed starting containers, like egg cartons, Dixie cups, and yogurt cups. Just wash them out and poke a few drainage holes in the bottom with a nail or an awl.
Step 2: Fill your pots or trays with seed starting mix.
Dump your seed starting mix into a large tub or bucket, pour in a generous amount of water, and stir it up with your hands or a trowel.
As the seed starting mix starts to absorb the moisture, add more water as needed. (This will take several minutes, as peat-based seed starting mixes are slow to absorb.) You want the mix to be uniformly damp, like wet sand.
Fill your seedling pots with this pre-moistened seed starting mix.2
Step 3: Sow your seeds.
Place two to four seeds on the surface of the seed starting mix, and gently press the seeds down so they’re nestled in nicely.
If your seeds are very small, like basil or mustard, you can leave them uncovered.3
If your seeds are larger (like beans or peas) or they require darkness to germinate (check the instructions on the seed packets), cover them with a layer of vermiculite or seed starting mix equal to their height, usually 1/4 inch to 1/2 inch.
Step 4: Label your newly planted seeds.
Label each pot. Trust me, you will never remember what you planted where, as most seedlings look the same at birth.
At this early stage, cheap plastic plant markers work very well and stay out of the way, so save your big and beautiful metal plant markers for the garden.
Step 5: Keep your seeds moist and warm.
Mist your seeds with water.4
Assemble your pots in a seed tray (or reuse a disposable aluminum roasting pan, a baking pan, even that plastic clamshell that your salad greens came in) and cover with a humidity dome (or just plain old plastic wrap).5
If your dome has vents, keep them open to help with air circulation during the sprouting period.
Now, you need to add heat. Since sunlight is not essential at this point, your seed trays can be placed wherever it’s warmest in your house, such as an attic, bathroom, laundry room, or kitchen.6
If your seedling pots stay covered in a warm nook, the low humidity will keep your seeds happy until they sprout. High humidity will make them sad. Only spritz the seeds with more water if the mix feels dry to the touch.7
Within a couple of days to a couple of weeks, the seeds will germinate. As your seedlings start to emerge, some of them will look like they’re wearing little seed hats.
Germination (the process of a seed sprouting) is highly variable, so don’t stress if it feels like it’s taking forever to happen. In most cases, seeds will germinate within three weeks (after that, try starting a new round of seeds).
Step 6: Give your new seedlings light.
At this stage, the newly germinated seedlings need light. Remove the humidity dome or plastic wrap, and move the seedlings to the sunniest spot in your house (preferably a south-facing window).
Continue to keep the mix moist, but not overly wet. Seedlings should be watered once a day or every other day, depending on how much sun and heat they get.
Remember that seedling roots are fairly close to the surface and they’re growing in a small amount of media, so they don’t need a deep soak the way larger plants do.
I like using spray bottles or squirt bottles, as the gentle streams of water won’t displace seeds or damage seedlings.
Step 7: Moving day! Transplant the strongest seedlings when they’re ready.
After your seedlings develop their first “true set” of leaves, they are ready to be transplanted.8
If more than one seed sprouted, choose the strongest one and pinch or snip off the others. You can even keep all of them, but be careful separating the roots if the seedlings are close together.
Transplant the seedling into a larger container filled with potting mix. Hold it by the cotyledons (the first leaves that appear) and try not to manhandle the tiny roots.
At this stage, you can lightly drench the potting mix using a diluted solution of compost tea or all-purpose fertilizer. Keep it simple, keep it organic, and don’t obsess too much over the nutrients.9
Give the seedling plenty of sunlight each day (at least 12 to 16 hours is optimal for most vegetable seedlings) to avoid the “leggy” look. (Learn how to fix leggy seedlings if this is happening to you.)10
Step 8: Harden off those seedlings.
Over the next week, move it from diffused sun to partial sun to full sun, and for longer periods of time, until it’s finally kept outside all night.
Step 9: Transplant your seedlings outdoors.
After the hardening off period, you can transplant your seedling to its final destination, whether straight into your garden or into a larger container.
And then, in a couple of months, you can enjoy the fruits (and veggies) of your loving labor!
1 This seems obvious, but laziness gets the best of us. Clean pots are key and help keep damping off at bay (an untreatable fungal disease that causes seedlings to suddenly keel over and die at the soil line).
Discard or thoroughly wash any pots that previously housed diseased plants. Avoid using leftover soil from the nursery container you brought home, as it might harbor weed seeds and bad bacteria.
If you have a healthy garden, you can skip washing your pots and simply dump out the dirt from your pots before using again.
I’ve put countless seed trays and humidity domes to the test over the years, and found these trays and domes to be the thickest and strongest on the market — they don’t bend, flex, or crack as easily as other brands, and can be reused for many seasons. back
2 It’s easier to start with pre-moistened mix, as peat-based mixes are harder to wet down uniformly if they dry out in pots. Although peat has a very high water-holding capacity once it’s wet, it actually repels water when it’s dry. Go figure.
If you’re not using homemade seed starting mix, this is a reputable brand that I like. You do not need anything fancy; seeds just need a basic mix of perlite, vermiculite, and peat moss (or coco coir) to germinate and grow into healthy seedlings. back
5 This creates a greenhouse effect to keep your seeds moist and warm, the key to germination. Most annual vegetables germinate best in temperatures of 75°F to 90°F. A few, such as radish, will germinate at lower temperatures.
Seeds will sometimes sprout in less than ideal temperatures, but the germination period will be longer. back
6 I like to put my seed trays next to my heating vent on the floor. Some gardening guides suggest placing your tray on top of a refrigerator, but most appliances these days are energy-efficient and do not give off much heat. back
7 Too much water will make the seeds rot. If your makeshift greenhouse is looking a bit too wet inside, remove the cover or plastic wrap for a few hours during the warmest part of the day to allow air circulation. Mold is no good for seeds, either. back
8 The true leaves are actually the second set of leaves that appear; the first leaves that initially unfurl are not leaves at all, but cotyledons. These leaf-life structures are part of the embryo of the seed, and supply food to the seedling until its true leaves begin the process of photosynthesis. back
9 I like to use home-brewed compost tea or liquid sea kelp. No fertilizer is fine, too, especially if you start with good soil. I have grown healthy vegetables with no fertilizer through a whole season, and could barely keep up with the harvests. back
10 It sounds sexy, but it makes your seedling tall and weak as it channels its energy into straining for sunlight. I also like to gently run my hands across the top of my seedling to simulate a breeze; this slows down initial growth and strengthens the stem. A few brushes a day is all it needs. back
Where to buy indoor seed starting supplies
Bootstrap Farmer Multi-Color Extra Strength Seedling Trays | Bootstrap Farmer Extra Strength 1020 Propagation Trays | Bootstrap Farmer 32-Cell Seedling Starter Tray | Bootstrap Farmer 32-Cell Seedling Starter Tray with Inserts | Bootstrap Farmer Humidity Dome | Koram Seed Starter Trays with Lid and Base | Behrens Galvanized Steel Pail | Black Gold Seedling Mix | Hoffman Canadian Sphagnum Peat Moss | Hoffman Horticultural Vermiculite | Hoffman Horticultural Perlite | Kinglake 4-Inch Plastic Plant Marker | Staedtler Lumocolor Permanent Garden Marker
What to know after your seeds germinate
- What is Damping Off Disease?
- Leggy Seedlings: What Causes Them and How to Correct Them
- How to Harden Off Your Seedlings
- Why Do Multiple Seedlings Sprout From a Beet Seed?
This post updated from an article that originally appeared on March 19, 2011.