Pick a recipe and combine ingredients in a large sterile tray, pot, or bucket.
Easy seed starter mix: 1 part sphagnum peat, 1 part vermiculite, 1 part perlite (parts by volume, not weight)
Cornell University seed starter mix: 2 parts peat moss, 1 part perlite, 1 part vermiculite (parts by volume, not weight), 1 teaspoon lime, 1 teaspoon 0-20-0 fertilizer, 2 teaspoons 19-6-12 fertilizer (slow release)
Why not use garden soil?
Dear Tomato Dirt,
Can I use soil from my garden to start my tomato seeds? I think it might save me some money.
Garden soil is not sterile. Try to avoid using it if possible because it’s full of weed seeds, it compacts (preventing good circulation), and worst of all – it contains nasty disease-carrying organisms, bacteria, and fungi, which have a bad reputation for causing damping-off disease.
If you must use garden soil, sterilize it before planting. Place soil in a shallow pan. Bake at 180°F for 45 minutes. Make sure soil reaches 180°F so all the nasties are zapped. But don’t overcook, or you’ll release toxins in the soil.
What to do after choosing a starting mix
Whichever potting mix you use, make sure you moisten it well. Add warm water and stir with a sterile trowel or large wooden spoon until the mixture is evenly damp, like a wrung-out sponge. Press it lightly into your seed starting containers.
Keep extra sphagnum peat moss on hand when growing tomatoes from seeds and sprinkle it on top of your prepared seed cell trays. Its anti-fungal properties are helpful in keeping seeds and seedlings disease-free.