Demeter was the goddess of growing plants.   Together, Demeter and Dionsyus were considered gods of the harvest. She is the cause of the seasons.  This happened when Hades stole Demeter's daughter, Persephone, to marry her.  While Persephone was gone, winter lasted for a year because Demeter was mourning.  When Persephone was in the underworld, she ate six pomegranite seeds.  She could only go back to her mother six months out of the year because of this.  While Persephone is gone, Demeter mourns and winter comes.