Tu B'Shevat is a minor holiday intimately connected to the agricultural cycle of the land of Israel. The "New Year of Trees" falls on the 15th day of the Hebrew month of Shevat. The holiday is often celebrated by planting saplings and participating in a seder that echoes the Passover meal but features fruits and nuts.
The Hebrew Bible expresses a great reverence for fruit trees as symbols of God's bounty. According to a rabbinic teaching, when God led Adam around the Garden of Eden, God said, "Look at my works. See how beautiful they are, how excellent! For your sake I created them all. See to it that you do not spoil or destroy my world, for if you do, there will be no one to repair it after you" (Ecclesiastes Rabbah 7.13).
In light of this special connection between the Jewish people and the land of Israel, special laws were formulated to protect fruit trees in times of war and ensure that the produce would not be picked until the trees were mature enough. 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 the trees. Once the trees turned four years old, Tu B'Shevat served as the day on which farmers offered their first fruits to the Temple. The following Tu B'Shevat, the farmers were then allowed to begin eating or selling the produce.
Tu B'Shevat lost relevance after the destruction of the Second Temple in 70 CE since there were no longer Temple priests to receive them. But Jewish mystics of Safed rediscovered it in the Middle Ages and created a new celebratory ritual called the Feast of Fruits . In 1753, kabbalists produced a Tu B'Shevat Haggadah complete with biblical and rabbinic readings called "Pri Etz Hadar," or "Fruit of the Goodly Tree."
With the rise of Zionism in the late 19th century, the holiday became an opportunity for agrarian pioneers to celebrate their efforts to restore the fertile ecology of ancient Israel, which had been damaged over centuries of repeated conquest, destruction and desertification. Today, the holiday is regarded as a celebration of the environment, a way to link Jews with the land of Israel and a connection to contemporary ecological issues.
Tree planting takes center stage in Tu B'Shevat celebrations. Many American and European Jews contribute money to plant trees in Israel or plant them in their own communities. In climates where tree planting is not feasible, Jews sometimes plant seeds for parsley  that will eventually be used on Passover seder plates.
With increased concern for the environment in recent years, Tu B'Shevat has taken on additional meaning as a day when Jews act on their concern for the ecological well-being of the world in any number of ways.
Tu B'Shevat seders have also become increasingly popular. Modeled after the Passover seder, the Tu B'Shevat ritual often includes readings from the Hebrew Bible and rabbinic literature. According to the kabbalistic tradition, participants drink four cups of wine: white, to symbolize winter; white with some red mixed in, a harbinger of the coming of spring; red with some white, to represent early spring; and lastly, all red, to correspond to spring and summer.
The seder incorporates seven fruits and nuts associated with Israel as the "land of wheat and barley, of vines, figs and pomegranates, a land of olive trees, and date-honey" (Deuteronomy 8:8). Kabbalists also gave almonds a prominent place in the seder since almond trees were believed to be the first of all trees in Israel to blossom. Carob, also known as bokser or St. John's bread, became another popular fruit to eat on Tu B'Shevat, since it could survive the long trip from Israel to Jewish communities in Europe.