Start seed indoors 5-7 weeks before last frost. Provide plants with plenty of light to avoid tall, spindly tomato transplants. A sunny south-facing window or grow lights will be sufficient. A heat mat helps to speed up the germination process. Optimum soil temperature for seed germination is 65-85 degrees. A few weeks before transplanting time, harden off plants by exposing them to an increasing number of hours outdoors each day. Delay transplanting until your soil has thoroughly warmed up in the spring; usually about 2 weeks after the your average last frost date. Set transplants in the ground and cover stem so that only 2-3 sets true leaves are exposed, resulting in a stronger root system.