The Talmud, Judaism’s Oral Tradition which was written down and compiled after the fall of the Second Temple, teaches that there are four “New Years” on the Jewish calendar. Each of these New Years are important because they have ramifications in Jewish law and have spiritual significance as well.
The first of the Hebrew month of Nissan, which is in the spring, is the New Year for Kings, and is tied to the counting of the reigns of the kings. It is also closely associated with the season of Passover, and is considered the anniversary of the founding of the Jewish people after their redemption from slavery in Egypt.
The first of the Hebrew month Elul, which is in late summer, is the New Year for tithing of cattle during biblical times. While this New Year is not observed today, the month of Elul does mark the beginnings of preparation for the High Holy Days. A month later in early autumn, the first of the Hebrew month Tishrei is the New Year most people are familiar with: Rosh Hashanah, the Jewish New Year that commemorates the creation of the world.
Tu B'Shvat is a Jewish holiday that is considered the New Year for Trees. Tu stands for the number 15, and Shvat is the name of the month in which the holiday falls. The fifteenth of Shvat, which falls in the winter, is the official date of this New Year.
Why is this particular time in the dead of the winter designated the New Year for Trees? It would seem that the spring, when the trees blossom and bloom, would be a much more appropriate time. Or perhaps even autumn, when the trees display their brilliant colors as one season comes to an end and the next begins. Winter, however, when we celebrate the life of the trees, is a time when the trees seem least alive. Many are completely bare and look all but dead.
To understand why the 15th of Shvat is the New Year for Trees, we have to look beneath the surface. Literally.
It takes about four months for the rains of the Jewish New Year to saturate the soil and enter the trees. In Israel, the rainy season begins just after Rosh Hashanah. Any fruit that is produced between Rosh Hashanah and Tu B'Shvat is considered last year’s fruit since it was created by the rains of the past year. Anything produced four months later, after Tu B'Shvat, is considered fruit of the New Year.
So Tu B’Shvat is literally the New Year for the Trees because it is only from that point forward that the trees are infused with the water from the New Year.
This actually has a lot of practical implications in biblical law. It affected the laws of tithing fruit when the Temple stood (Deuteronomy 26), it has implications on the Sabbatical year which is still observed in the land of Israel today (Leviticus 25), and it determines the biblical prohibition of eating fruits of new trees for the first three years (Leviticus 19:23).
Moreover, while we can’t see it in the winter, beneath the surface the trees are very much alive. It is now that they begin their cycle of life. Underneath the cold and sometimes frozen ground, the new sap in the trees begins to flow. This is the beginning of the process that will produce the buds, blossoms, and flowers that we enjoy in the springtime.
To celebrate the trees and their fruit on Tu B'Shvat it is customary to have a festive meal with fruits, preferably those included among the seven species of the Holy Land: grapes, figs, pomegranates, olives, and dates (Deuteronomy 8:8). Some people even have a Tu B'Shvat seder, which like a Passover meal has four cups of wine, a text that is recited together, and special foods – in this case 10–15 specified fruits – to be eaten in service of God.
In contemporary Israel, Tu B'Shvat has also become a kind of Arbor Day, when trees are planted all over the country in celebration and joy.