Tomatoes are a favorite crop for home gardeners, typically grown during summer in most climates. Many home gardeners simply purchase nursery-raised tomato plants to transplant into their gardens, but this can become expensive when you're raising many tomato plants, or want to raise a specific variety. Since one packet of seeds usually costs less than one tomato plant, you'll be able to grow many more tomato plants for your garden when you start plants from seed. Tomato seeds need the right kind of growing mixture, temperatures and moisture in order to germinate properly.
Start your tomato seeds about six to eight weeks before the last expected frost. Fill seed flats or 2- to 3-inch-diameter pots with a sterile seed-starting potting mix or a mixture of three parts pasteurized potting soil, two parts peat moss and one part perlite.
Plant the tomato seeds 1/4-inch deep into the potting mix. Plant one tomato seed per flat or two to three seeds per pot.
Water the seeds lightly to evenly moisten the potting mix. Cover the flats or pots with a plastic bag to preserve soil moisture and warmth.
Keep the potting mix warm while the seeds are germinating at a temperature between 75 to 90 degrees F.
Move the tomato seedlings after they sprout into full, direct sunlight, such as beside a south-facing window. Keep air temperatures between 60 to 70 degrees and rotate the plants each day, advises University of Missouri Extension. Continue watering the tomato seedlings lightly once every two or three days to keep the soil fairly moist.
Transplant the tomato seedlings into 4-inch-wide pots when they develop their second or third set of mature "true" leaves. You should transplant the seedlings before they become completely root-bound in the smaller pots or flats.
Transplant the tomato seedlings outdoors in spring, after all chance of frost has passed and the soil has warmed up to at least 60 degrees. The tomato plants are ready for outdoor transplanting when they're about 8 to 10 inches tall and have stocky, healthy stems.