Tips for How to Germinate Seeds Indoors

Tips for How to Germinate Seeds Indoors

Reading Time: 8 minutes


Need some tips on how to germinate or start seeds indoors? Learn how; from trays to testing seeds to soil.

By Gail Reynolds – There’s probably nothing quite so rewarding for any gardener as the success of starting your own herb, vegetable, or flowering plants, indoors, from seed. Not only can you get an early jump on the growing season by growing seedlings indoors, but you can realize some serious savings in the process.

For the commercial grower (even the small-scale truck gardener or farmer’s market vendor) germinating seeds indoors is not simply the most cost-effective way to go, but producing (rather than purchasing) your own plants can usually make the difference between red or black ink in the profit margin at the end of the season.

For the home gardener, there are some major bucks to save as well when you pit the relatively small investment for your time, effort, and seed purchases against the prevailing retail prices for plants.

For example, I’ll grow herbs from seed here since I know them best. For a packet of approximately 100 herb seeds (even the rarest varieties) fall in the neighborhood of $1.50 from top seed companies. The retail catalog price for one plant (even the most ordinary) is around $4.50, not including shipping.

In any event, the real satisfaction of germinating seeds indoors comes in the freedom to select those plant varieties and cultivars which best meet your needs for taste, appearance, quality, and productivity, instead of being limited to only those selections available on the nursery shelves or through catalog offerings.

While germinating seeds indoors can be challenging, once you’ve got the principles of successful germination down pat, it’ll soon become old-hat! I’ll try and share some of the stuff we’ve learned over the years (through not only our successes but our outrageous failures, as well), plus hopefully put you on to some money-saving tricks to avoid any top-heavy initial investment.

Getting Started Germinating Seeds Indoors

The first lesson is to get started at the right time. If you are wondering when to start vegetable seeds indoors, charts and lists will tell you to start germinating seeds indoors six to eight weeks before your usual outdoors planting time. Before we get into what you’ll need, become acquainted with the folks who run your local privately owned plant-sales (not plant supplies) nursery or a commercial grower in your area. Generally speaking, these folks will be excited about what you’re doing; they’ll offer some invaluable tips for germinating seeds indoors and be there to troubleshoot if you run into any problems; plus they can help supply you with the standardized best in equipment at a nominal cost.

The reason for this is that commercial growers, such as ourselves, purchase seeding equipment at wholesale prices in case quantities. More often than not, it is more cost-effective for us to purchase that case-volume (even if it’s more than we need) than to purchase a lesser volume at the per-single price.

For example, we purchase our 20-row seeding trays in the 100/case volume at under 50-cents apiece. Retail single unit price can get as high as $1.50 and $2.00. I doubt I’ll live long enough to use all of our seeding trays so I’m not averse to selling one or two of them to someone at our going-in price, just to recoup some of our original outlay.

Furthermore, many of these nursery plastics are reusable, if rinsed in bleach water from year to year. So I might simply give away a few used ones and start the season with some brand new ones!

Here’s what you’ll need to get started: Containers for germinating seeds indoors, soil mix, watering can, water sprayer or mister, labels, underneath heat source, permanent indelible pen or marker, and seeds.

Containers: You can start seeds in practically any type of container that will hold a couple inches of starting soil mix — from an egg carton seed starter to commercially available pots, open flats, or compartmentalized flats.

how -o-germinate-seeds
Nearly any shallow container will work for starting seeds.

The main thing when it comes to containers (particularly for germinating seeds indoors) is that they won’t become easily waterlogged, are shallow enough to readily absorb heat from overhead and underneath sources, and are compact in size.

For germination, you’ll want to maintain a steady overhead and underneath temperature of 75-90 degrees for about two weeks. When your plants reach the seedling stage and are ready to be transplanted into larger containers, temperature requirements can be relaxed and are less critical.

Since you’ll be shelling out for the heating expenses, it only makes sense to focus your heat sources on the smallest amount of area possible. My pick: A 20-row seeding tray (placed into an open flat). Because of its shallow trenches, this seeding tray lends the best environment for quick, healthy seed germination. And because of its compactness — you can start as many as 1,000 seedlings in this single 11×21-inch piece of equipment — it saves lots of space and heating costs. Retail costs for seeding tray and flat: $3-$4.

Soil mix: While some authorities would recommend one soil mix for germinating seeds indoors and another compound for your transplants, I find this a waste of money, since you can find soil mixes which satisfy both needs well.

My pick is Metro Mix 366 (2.8 cu. ft. bag). A bag of this will fill your one seed tray plus 19 transplant trays (called 1204s-each tray houses 48 separate transplants). In the lesser alternative, I’d vote for Schultz Potting Soil (in the same capacity). Cost for either is around $7.50. Caution! Do not use ordinary garden soil and steer away from potting soils on sale outside your corner grocer or discount outlet. These look like a steal of a deal, however often times they are so dense that they eventually choke off and kill your transplants. One year, in desperation on a Sunday, we purchased some and lost about 5,000 of our basil plants in the experience.

Bottom heat source: This can be anything from a 25-watt light bulb in an apple box placed below your seeding flat to a heating blanket or heating pad.

My pick is a heating pad (pick one up at a garage sale) which fits perfectly underneath your 11×21-inch flat.

Overhead heat source: If your house is fairly toasty (and since heat rises) once you’ve seeded your tray, try placing the whole germinating deal on top of the refrigerator or a cabinet for a couple of days until you see the first sprouts popping up. After that, you’ll want to expose the flat to light.

Water source: A watering can will allow you to initially wet down the soil you have placed in your seed tray (let water completely absorb before you distribute seeds) and use later on your transplanted seedlings. You’ll need a mister (an old cleaned out window-spray plastic bottle works wonderfully) to water the newly germinated seeds and sprouts for about two weeks until they’re ready for transplanting.

Seeds: Steer away from too-good-to-be-true 10 seed packets/$1 deals. Generally, you’re lucky if you get 15-25 seeds and exceptionally lucky if any of them ever germinate.

My pick would be a reputable seed house. You can get some pretty good mini-packet prices for quality seeds, which you can seed out and label in each or any of the 20 separate rows of your seeding tray.

Markers and labels: I use popsicle sticks for stick-up labels to mark what I’ve seeded in each row. They fit in the ends of the seed rows perfectly and they stand tall enough for me to read. As far as marking pens, just make sure they’re permanent markers or your water misting will remove what you worked so hard to put on.


Editor’s note: Prices from 2003.

The How-To of Seeding

First place your soil mix into your container, flush to the top. Water it down generously, and let it absorb fully. If you’re using the 20-row seeding tray, place it in the open flat once all water is absorbed. Sprinkle your seeds on top of the moistened soil. In the 20-row seeder, you can seed 50 seeds per row. Label your row each time you change plants or varieties of a plant. If you have more than one seeding tray or container and do not seed all at the same time, you may want to place the seeding date on your label as well, so you can track the germination time.

Unless the instructions on your seed packet tell you not to, sprinkle some of the dry soil mix over the top of your seeds to cover them. (Most seeds prefer to germinate in the dark.) Then take your index finger and tamp down this topping soil lightly to set seeds. Now, sprinkle with the mister until totally moist.

If your home is fairly dry (as ours is from wood heat), place your seeding tray or container inside a large plastic bag and secure with a clothespin or large paper clip at the open end.

Get your bottom heating source set up, place your container on top, and mist the soil whenever it appears to be drying out, then watch for the sprouts to poke through.

Rule of thumb for misting: Neither flood your soil mix nor allow it to dry out. While germinating seeds indoors, lean on the side of more moisture, rather than less if you are unsure. Later, during the seedling and transplant stage, do the reverse. Too much moisture will ruin your young plants (I’ve been there). Once your seeds have sprouted, they will need light, air, and moisture.

Light required is optimum 16 hours per day, and 12 hours is the absolute minimum tolerated for healthy seedlings and transplants. Natural light from a window is great — just make sure there’s no cold air coming from your window space.

If you’ve had plastic bags over your containers, the time to remove them is when the sprouts begin to pop through the soil. Leave them in open air and keep moist, then introduce the tender sprouts to at least some light at intervals during the daylight hours, keeping them free of chill. Keep moist and continue to provide a heat from underneath, as well as in the surrounding air.


The first leaves to unfold when a seed germinates are called “cotyledone.” These first leaves often look different from the leaves that follow. Those that follow are considered “true leaves.” When seedlings develop their first set of true leaves, they are ready for transplanting.

You can transplant your seedlings into any type of container you wish. We transplant ours in 1204 trays, which house 48 separated plants per 11×21 plastic container. This tray is placed into an open flat.

Whatever container you choose to use, make sure it has proper drainage. You may wish to buy commercial plastic trays (such as the 1204) and place some gravel above the drainage hole in the bottom of the container for proper filtering. Fill the container with the appropriate potting soil, water down completely, and let the soil completely absorb the water.

Once the soil has absorbed the water, take a popsicle stick (or old pencil) and place a circular hole wherever you intend to place a seedling. (In the case of the plastic compartmentalized trays (such as the 1204), place one hole in the center of each compartment.

Now, with your index finger, carefully lift out a portion of seedlings from your germination container. In the case of the 20-row seeding tray, lift out about a one-inch portion of a row, scooping it from the bottom. Carefully, separate the seedlings (from the bottom side-not the top and not the root), taking each seedling and gently poking it into the holes you have just made. Allow for at least one-third to one-half of the seedling below the soil mark. Take your thumb and forefinger and gently squeeze the soil around the plant and go on to the next one. Once you get the hang of this it all goes very quickly and smoothly.

Once your transplanting is completed, you can lower your temperature requirements (60-70 degrees is fine), remove any bottom heat source and begin to watch your plants flourish.

You can now water with your watering can, preferably one which can “sprinkle,” rather than “pour” the water into the container.

Do not over-water however, and do not allow the soil to completely dry out.

Prior to planting outdoors, it helps to harden off your transplants. For a few hours during the warmth of the day, set them outside and allow them to acclimate to the outdoors.

When the plants are anywhere from six to eight weeks old, your outside area is free from frost and the soil temperature reaches a steady 50 degrees, you’re ready to plant these puppies outdoors.

Have fun and good luck germinating seeds indoors!

Published in Countryside March / April 2003 and regularly vetted for accuracy.

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