Seedlings started indoors in newspaper pots
Garden of Eatin', How-To, Seeds & Seedlings

The No-Brainer Guide to Starting Seeds Indoors

Exactly as the title says — this is an easy and foolproof guide to starting seeds indoors.

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. Growing seedlings 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.

This simple step-by-step 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.)

We’ll start with the basics of what you should gather:

  • Seeds
  • Seed starting pots or cell trays
  • Seed starting mix
  • Seed tray with humidity dome (often called a 1020 plant tray, propagation tray, or germination station, or use any DIY drainage tray with plastic wrap)
  • Spray bottle filled with water

If you’ve already made your recycled newspaper pots, you’re all set. If you’ll be using other seed starting pots or cell trays, make sure they’re clean.1 You can also repurpose household items like egg cartons, Dixie cups, and yogurt cups — just wash them out and poke a few drainage holes in the bottom.

Fill your seedling pots with pre-moistened seed starting mix.2

Place two to four seeds on the surface, and gently press the seeds down so they’re nestled into the mix. 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, cover them with a layer of vermiculite or seed starting mix equal to their height, usually 1/4 inch to 1/2 inch.

Label each pot. Trust me, you will never remember what you planted where, as all seedlings look the same at birth.

Label all your seedlings

Mist your seeds with water from a spray bottle.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 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.

Cover seedlings with a dome to simulate a greenhouse effect

Keep your plastic dome vented for air circulation

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 (depending on seed variety), the seedlings will start to emerge. They’ll look like they’re wearing little seed hats.

Seedlings emerging

Now, they need light. Remove the humidity dome or plastic wrap, and move the seedlings to a sunny spot in your house, such as a south-facing window. Continue to keep the mix moist, but not overly wet.

After your seedlings develop their “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 ideal for most vegetable seedlings) to avoid the “leggy” look. (Learn how to fix leggy seedlings if this is happening to you.)10

You can start to harden off the seedling11 by moving it outside under diffused light for a few hours and bringing it back inside each night. Over the next week, move it from diffused sun to full sun, and for longer periods of time, until it’s finally kept outside all night.

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!

Footnotes for the Curious

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 the wash 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. back

3 For certain varieties of plants, light will often speed up germination (the process of a plant sprouting from a seed). back

4 The moisture will help the seeds shed their protective coating and eventually sprout. 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 wall heater. 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

11 Hardening off is the process by which you gradually acclimate the seedling to its future environment outdoors… getting it acquainted with the breeze, the birds, and the bees. back

Project Sources

Bootstrap Farmer 1020 Tray | Bootstrap Farmer 32-Cell Seedling Starter Tray with Inserts | Bootstrap Farmer Humidity Dome | Dr. Earth Root Zone Seed Starter Potting Mix | Kinglake 4-Inch Plastic Plant Marker

This post updated from an article that originally appeared on March 19, 2011.

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