Tomato growing season varies largely based on location, but most places in the United States have a growing season that begins sometime between mid- to late April and May. Based on when cooler weather arrives in a particular area, the growing season typically ends somewhere between September and October.
Because the growing season is short in many areas, tomatoes are typically planted from starts when the soil is warm enough for the plants to thrive. This allows for adequate fruiting and ripening before the season ends. Tomato season typically ends in most places when the temperatures cool and the days become shorter.