This article from My Jewish Learning traces the evolution of the holiday of Tu B’Shvat, beginning with its halachic roots in Temple times through the different ways in which it was interpreted by the 16th century Kabbalists in Tsfat, the Zionist pioneers of the 19th century, and the modern environmentalists of today. Each group focused on different aspects of this day and celebrated with corresponding rituals, including a mystical Seder, eating fruits from the Land of Israel, and planting trees in Israel and around the world.