Tomatoes are a warm-season annual that grow best when the soil temperature is at least 55°F and the air temperature ranges between 65° and 90°F. Tomatoes require from 50 to more than 90 warm, frost-free days to reach harvest.Tomatoes are commonly grown from seedlings started indoors and transplanted into the garden.row young seedlings on at 60° to 70°F; allow a gentle breeze to rustle over young seedlings each day so that they grow strong stems. About four weeks after germination, about two weeks after potting up seedlings the first time, pot them up again to 4-inch pots.