26. The fifteenth day of the month of Shevat (Tu Bi'Shevat) is the new year
("Rosh Hashana") regarding trees (1). The Tachanun prayers are not recited,
and it is customary to partake of different types of fruits
(1) The opening Mishna of tractate Rosh Hashana lists a number of dates
throughout the year which serve as the transition to a new year in terms of
certain halachic issues. For example, the first day of Tishrei is viewed as
the new year in terms of G-d's judgement, and hence the "Day of Judgement"
is also called "Rosh HaShana." Similarly, the fifteenth of Shevat marks a
new year for trees in that tithes ("Ma'aser") taken from fruit which
blossomed before the fifteenth of Shevat, cannot exempt (from tithing)
fruit that blossomed after the fifteenth.