The best time to start growing tomato plants is in the spring. While planting times may vary depending on local climate, outdoor seeds should be planted once temperatures are expected to stay above 50 degrees Fahrenheit.
Tomato seeds should be planted indoors between six to eight weeks before the average date of the last spring frost. Soil should be well plowed and prepared with compost before sowing seeds outdoors or transplanting plants to a garden. Soil temperatures of at least 60 F are ideal for outdoor planting. Most varieties of tomato plants mature within about 100 days, although some species may require as little as 50 to 60 days.