Tomato seeds can be started in pots, peat pellets, or flats. Be sure there are holes in the bottom for drainage.
Use a sterilized planter mix. A sterilized, pasteurized soil, or commercial seed starting mix will be free of weeds and fungi that cause seedlings to collapse and die.
You can pasteurize your own garden soil: bake the soil in a shallow pan at 200F for an hour or two (smell will be bad). If you place a potato in the oven with the soil, the soil will be sterilized when the potato has baked.
To make you own seed starting mix, combine equal parts sand, vermiculite or perlite, and peat moss.
Treat seed saved from last year’s garden for disease resistance. Soak the seed in a mixture of water-soluble fertilizer for two hours before planting. This seed will be heavier rooted and healthier. Most commercial seed has been treated.
If you sow seed in 3- to 4-inch clay or peat pots, fill the pots to ½ inch from the top.
Thoroughly moisten the seed starting mix before sowing to make sure it is not dry below the surface.
Sow seed ¼ to 1/3 inch deep; space seeds 1 inch apart. As a general rule, sow seed three times the depth as the width of the seed.
Sow twice as many seeds as you need plants so that you can later choose from the strongest seedlings.
Do not sow too deeply otherwise the seed may rot before it germinates.
Firm the seeds into the soil with a piece of wood or flat object; then add a thin layer about ¼ inch of moist soil mix over the seeds and level it and firm again. This will bring seeds into good contact with the soil which is important for germination.
Keep the seed starting mix or soil moist but not wet after sowing; gently water with a fine spray being careful not to wash away seed.
Seeds can be started in bright window or under lights set about 2 inches above the plants.
Maintain soil temperature between 75°F and 85°F; seeds will germinate in 7 to 10 days. To maintain an even soil temperature, use a propagating mat or rubberized “electric blanket” placed under starting pots, flats, or trays.
Place the seed-starting container inside a clear plastic bag or tent or cover the container tightly with a plastic sheet to retain moisture and warmth until the seeds germinate. You can also lay a piece of newspaper on the containers until seedlings emerge. To germinate seeds require warmth and moisture, not light.
Remove the plastic bag or sheet when seeds emerge.
When seedlings emerge, give them full sunshine or place them under grow lights. You can use two 48-inch, 40 watt fluorescent tubes placed a few inches above the seedlings. These can be supplemented with a couple of incandescent bulbs to provide the “red light” that growing plants need. Keep lights on sixteen hours a day when using fluorescent lights.
Set plants an inch or two below the fluorescent tubes and maintain that distance as the plants grow. If plants are too far away they will stretch and develop thin, weak stems. Plants must have lights off at least 8 hours a day to grow strong.
Check seedlings every day as they grow. Be sure to keep grow lights at a constant distance above the seedlings.
Seedlings growing in a window should be turned every day so that they do not develop a permanent lean–heliotropism means growing towards the sun.
Keep seedlings near a constant 70°F; temperature greater than 70°F may produce tall, spindly sprouts. Windowsills may get hot during the day and cold at night; seedlings grow best if kept at an even temperature.
Keep the soil moist, but not wet. Water or mist plants gently to avoid washing them out. Use room temperature water.
Do not fertilize seedlings right away; wait a week or two or until the first repotting, then mix in a small amount of balanced, water-soluble fertilizer in the plants’ water.
Seedlings grow best when day time temperatures are between 70°F and 75°F during the day and between 60°F and 65°F during the night.
Seeds can be started in a coldframe–a glass- or plastic-covered box, heated by solar radiation as long as the temperatures remain warm enough for germination and growth. Seedlings growing in a coldframe or greenhouse should receive 12 hours of sunlight each day.