Not surprisingly, there is no biblical reference to the holiday of  Tu Bishvat. Rather, the sources that describe this calendrical observance are found in the Mishnaic tractate, Rosh Hashanah, (the New Year). More on that later... 

In order to understand Judaism and its holidays, sometimes one must go beyond the Hebrew Bible. While the bible contains the scriptural basis for many of our holidays, not all are biblical in origin. This may sound confusing to those who have always thought of the Jewish people as the ‘people of the book'. In fact, we are the people of the books. Which books? The written law and the oral law. The written law refers to Torah, Prophets and Writings, or the Hebrew Bible; the oral law is commonly understood to mean the Mishnah and the Gemara, which together equal the Talmud. Although the Bible is considered more important than the Talmud, we make sense of Judaism through the eyes of the Talmud and rabbis. 

Essentially, we are not biblical Jews any longer; rather we are rabbinic Jews, or Jews who interpret the bible. We have holy books (Talmud) that give us guidance from the beginning of the most formative period in Judaism, the Rabbinic Period, which overlaps with the period of Jesus and the writing of the New Testament. 

Back to Tu Bishvat!  Tu Bishvat is literally translated as the fifteenth of the month of Shvat and corresponds to a time in the Jewish calendar when we begin counting a new year for trees. The Mishnah, edited by Rabbi Judah the Prince in approximately the year 200 of the Common Era, articulates four specific new years, and one of them is the new year for trees. The rabbis explained that this the time of year that the first fruits of the trees begin to form. We need this date in order to establish when fruit may first be picked and eaten, as we must wait three years for the tree to mature (orlah).  

Earlier I said that there is no biblical reference to the holiday of Tu Bishvat and that is correct. Tu Bishvat was originally not a festival. However, the impetus for this special date is derived from the Hebrew Bible in the book of Leviticus: "When you enter the land [of Israel] and plant any tree for food, you shall regard its fruit as forbidden. Three years it shall be forbidden for you, not to be eaten" (Leviticus 19:23). The rabbis read the bible very carefully and wanted to know how to count this three year period, hence the creation of the new year for trees, which gives us a starting point for this period. 

Perhaps the most well known custom for Tu Bishvat is tree planting.  Rabbi Michael Strassfeld, the author of The Jewish Holidays: A Guide & Commentary, writes the following:

In the twentieth century, because of the growth of  Zionism and then the founding of the state of Israel, the association of Tu Bishvat with the land of Israel has gained even more significance. In Israel the day is celebrated with elaborate tree-planting ceremonies held by schoolchildren. In the Diaspora, children and adults give money to the Jewish National Fund (JNF)to plant trees in Israel.

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If you happen to be in Israel during Tu Bishvat, you can participate in the important mitzvah of rebuilding the land and nation of Israel after a hiatus of two thousand years. JNF helps Israelis to plant, contribute to the infrastructure of the land and participate in activities that help us to be aware that God has appointed us as stewards of the earth and its environment.  

Recently, the Tu Bishvat Seder has grown in popularity. While this seder does not have the same traditions and rituals as the Passover seder, some customs have the participants drinking four cups of wine, 10 kinds of fruit, and discussing the transition from exile back to the land of Israel.  

On Tu Bishvat we celebrate this day that ties us to the land, its trees and its fruit, and we rejoice that the Holy and Blessed One has helped us to return to the Promised Land.