Tu Bishbat is the “new year of the trees.” This “new year or cycle” is an halakhic concept relevant to some commandments of the Tora related to agriculture. These precepts linked to land are called mitsvot hateluyot ba-arets “commandments that apply to the products of the land (vegetables, trees, grains),” and almost all of them belong exclusively in the land of Israel. For example: teruma (offerings to the Cohanim), ma’aser (tithes) shebi’it (resting of the land every seven years) etc.
Tu Bishbat is essential to know how old the trees are and determine thereby, for example, to which tithing cycle their fruits belong, as we will see below.
This tithe is like a “tax” of 10% from the harvest. There are two types of tithes. First, the ma’aser rishon, which was a tenth of the produce of the land giving to the Levites. The Levites did not own land to work, their function was to serve, along with the Cohanim, in the Bet haMiqdash and teaching Tora to the people. The Cohanim and Levites were the teachers and the rabbis of Am Israel, in the days of Bet haMiqdash.
Apart from this first tithe, for the first, second, fourth and fifth years of the seven-year cycle there was a second tithe or ma’aser sheni which was to be consumed by their owners in Yerushalayim. It could also de redeemed and exchange by other products to be eaten in Yerushalayim.
In the third and sixth years, the ma’aser ‘ani was given, this is the tithe for the poor. As we know there were many other gifts or tsedaqa given constantly to the poor besides ma’aser ‘ani. (See Maimonides MT matenot ‘aniim)
Now we can better understand the role of Tu Bishbat. Tu Bishbat is the cut off day that determines the age of trees and serves to determine to which cycle these fruits belong.
Another practical example of the application of Tu Bishbat is the commandment of ‘orla, the biblical prohibition to eat a fruit from the trees during the first three years after the tree is planted (Vayiqra 19:23). Tu Bihsbat is also the cutoff day for determining the end of these three years.
And why was Tu Bishbat established as the cutoff day for the trees? Our Rabbis explain that by Tu Bishbat most of the year’s rains have already fallen, the trees have absorbed the rain and now they exude resin with a new vitality, which represents the end of a cycle and the beginning of another.
One more thing about the mitsva of ‘orla. Unlike the tithes and other agricultural commandments that we have mentioned, the mitsva of ‘orla also applies outside of Israel. That is, when a Yehudi plants a tree, no matter the country he or she is in, the fruits of that tree cannot be eaten during the first three years (Shulhan Arukh, YD, 294: 8).