This holiday can be celebrated by planting trees, eating fruits, and having a Tu B’Shevat Seder, a ritual that began with the kabbalistic masters of the 15th century.
Tu B’Shevat is a holiday intimately connected to the agricultural cycle of the Land of Israel. Falling in the middle of the Jewish month of Shevat, the 15th day of the month is the New Year of Trees. Today, this holiday is often celebrated by planting saplings and also by participating in a seder-meal that echoes the Passover seder, in which the produce of trees, including fruits and nuts, are eaten.
Ideas and Beliefs
The Bible expresses a great reverence for fruit trees as symbols of God’s bounty and beneficence. Special laws were formulated to protect fruit trees in times of war and ensure that the produce of trees would not be picked until the trees were mature enough and tithes were given from them. In order to calculate the age of trees, both for determining when they could be harvested and when they were to be tithed for the Temple, the Talmudic Rabbis established the 15th day (Tu) of the month of Shevat as the official “birthday” of trees.
Subsequent to the destruction of the Temple, Tu B’Shevat lost much of its relevance, but in the middle ages it was rediscovered by Jewish mystics . In the modern period it has enjoyed another revival as a holiday that links Jews with the land of Israel and as a Jewish celebration of the environment .
Material excerpted from http://www.myjewishlearning.com/.