Step-by-Step Guide to Indoor Seed Starting

There's nothing like seeing the first seedlings breaking through the soil to get you excited for the coming spring. Photo: John Athayde via Flickr.

It's time! For those of us looking to get a jumpstart on the growing season, now's the time to begin thinking about starting your seeds. And if you're like me and you're going to grow onions, now is the time to start planting.

Below you'll find a step-by-step guide to growing seeds indoors. But first I wanted to talk dirt. No, not dirty. Dirt. Soil. Earth. Terra firma.

Your seeds need something to grow in. After pre-soaking them or pre-sprouting them, you have to put them in a medium to grow. Lots of gardeners simply use a store bought potting soil mix to get their seeds going, and that's a good start because it's a sterile medium. But I prefer going a different way.

There are typically two types of starting medium I like use: vermiculite or sand and sawdust. What? No dirt?

Nope. Well, at least not at first.

Soil-less soil
Most of the time I use an 8 oz. plastic cup filled just with vermiculite to get my seeds going. It's one of the easiest methods of getting my transplants growing that I've found.

Stack your cups together, turn them upside down, and drill a series of small drainage holes in the bottom so that you can water the seeds from the bottom and not disturb them. Fill the cups almost to the top with vermiculite and sprinkle as many seeds as you plan on growing onto the surface. Then cover them with an additional thin layer of vermiculite.

I always add 10% to 20% more seed than what my garden plan calls for just in case there's a problem with germination. If I get a high germination rate -- and using quality seed and taking the proper steps to get my seeds off to a good start, I often get 100% germination -- I still grow all the tiny plants because sometimes one or two can still suddenly die off. But once it becomes time to transplant them into the garden, I'll give the extras to a neighbor or toss them onto the compost pile.

With the seeds in their cups, I give them a good watering (again, from underneath) and then place them on a heat mat.

Keys to good germination
Seeds need two things to germinate: moisture and warmth. So after "planting" my seeds in the cups of vermiculite, I transfer them to my PVC seed starting grow station where I place them on a seedling heat mat.

The one I use is the Hydrofarm 9"x19-1/2" Seedling Heat Mat. I own six of them: four for my grow station and my wife wanted two for her own plants.



Once the seeds sprout, I immediately turn on the grow lights because the third component of a plant's life is light.

I just use regular fluorescent bulbs in a shop light housing. If I was going to be growing these plants indoors I'd probably get special bulbs, but because this is just to give the plants a head start on the season, I just use regular cheap bulbs. And I use a timer so that they're getting 16 hours of light daily.

Just make sure the seeds never dry out because that will kill them off faster than anything.

Once the leaves sprout their first leaves -- not they're first "true" leaves, but those the ones that appear soon after they break through the seed casing -- I transplant them into seed growing containers. In the past I've used plastic six-pack containers that you get transplants in from the nursery or local garden center, but this year I'm trying a 72-cell tray. We'll see how that goes.

Mel's Mix
But my soil medium is one of my own creation: equal parts compost, sphagnum peat moss, and vermiculite.

For gardeners familiar with the Square Foot Gardening method popularized by Mel Bartholomew, that growing medium is what he recommends and is commonly referred to as "Mel's Mix." However, while he says to use at least 5 different kinds of compost to ensure a complete, well-balanced soil for your seeds, I simply use the compost I make from kitchen waste and yard debris that's aged and sifted.

Because of the varied components that end up in my compost bins -- it's not just grass clippings and leaves -- I think it possesses a wide range of nutrients. And that's it! I've given the seeds as beneficial an environment to grow in and now it's time to sit back and wait.

A seed starting medium alternative
Now with all that being said, if I don't have vermiculite on hand to get my seeds going, I have used sand and sawdust with great results. You might want to consider it as a cheaper alternative to Mel's Mix as well. The one caveat though in using sand and sawdust to grow plants in is that it's basically inert. It has no beneficial nutrients so you'll need to fertilize the plants, whether with commercial fertilizers or organic sources.

Again, I only use that as an alternative in case I don't have vermiculite, and only before I transplant the seedlings into "soil" to grow in. But it is possible to do so, and it represents a much more affordable medium.

Step-by-Step Guide to Starting Seeds

Everything you need to begin starting seeds indoors

Supplies:

8 oz. clear plastic cups
Vermiculite (or other grow medium)
Seed starting station
Light source, like shop lights
Hydrofarm heat mat (optional)
Drill
1/8" drill bit







Step 1: Stack plastic cups upside down and drill series of drainage holes in bottom of cups.

Step 2: Fill each cup almost to the top with vermiculite, tap lightly to settle. Write the name of the seeds you're growing on the side of the cup, and maybe even the date if you wish.

Step 3: Sprinkle seeds on top of vermiculite.

Step 4: Cover seeds with thin layer of vermiculite

Step 5: Give your seeds a drink of water (they've had enough when the vermiculite uniformly turns a different color).

Note the different color of the vermiculite
as the water wicks its way up

Step 6: Place on heat mat.

Step 7: Watch for first signs of growth, then immediately transfer to light

Step 8: When seeds have their first set of leaves, transfer to a soil-filled seedling tray

Resources: 

Hydrofarm MT10006 9-by-19-1/2-Inch Seedling Heat Mat




Jiffy 72 Cell Professional Seed Starting Tray