This Saturday Say Happy New Year to a Tree
According to the Mishna (Tractate Rosh HaShonah, mishna 1), Tu b'Shevat is the New Year of the trees. Not all trees, mind you. Newly planted saplings, for their first three years, celebrate their New Year on Rosh HaShonah, the first day of Tishrei, along with the rest of creation. A tree planted more than 45 days before Rosh HaShonah is considered one year old on Rosh HaShonah. (If planted later than that, the tree belongs to the next year.)
For the first three years of a sapling's life, halachah (Jewish law) prohibits the eating of its fruit, which are called "orla." Once a sapling has seen Rosh HaShonah three times (or four times if it was planted less than 45 days before Rosh HaShonah), it is considered a tree, and Tu b'Shevat becomes its New Year. Fruit ripening after Tu b'Shevat of its fourth year is permitted to be eaten. (In the Land of Israel, when the Temple existed, the fruit of the fourth year was brought to the Temple, to be eaten there by the owner of the tree and his family and friends as a thanksgiving offering.)
Tu b'Shevat is also relevant to the biblical laws of gifts to the priests (terumot), tithes given to the poor and the tribe of Levi (maaserot), and the agricultural sabbatical year (shmittah), because the year to which tree fruit belong depends on whether they ripened before or after Tu b'Shevat.
The Talmud likens man to the tree of the field. Just as Tu b'Shevat represents a time of renewal for trees, after most of the winter rains have fallen, so too Tu b'Shevat should remind us to renew and revitalize the pledges we made to God and ourselves more than four months ago, on Rosh HaShonah.
So this Shabbat, say Happy New Year to a fruit tree. And eat some fruit, preceded by a blessing of course.