When sowing tomato seeds indoors, plant them about 1/4 inch deep in a shallow growing tray filled with seed-starting mix. Artificial light (grow lights) and heat mats are key elements to success because tomato seeds require warm soil to germinate. The soil should be at least 60 degrees Fahrenheit at all times. Once seedlings emerge and develop at least two sets of true leaves, transfer the seedlings to small pots. When they reach about 4 inches tall, plant them in their permanent large container. When planting a young tomato plant, remove the bottom set of leaves, and bury the stem up to the new bottom set of leaves. Roots will form all along the stem, resulting in a stronger plant.