- Is the day that marks the beginning of a "New Year of the Trees". This is the season in which the earliest-blooming trees in the Land of Israel emerge from their winter sleep and begin a new fruit-bearing cycle.
Legally, the "New Year of the Trees" relates to the various tithes that are separated from produce grown in the Holy Land. These tithes differ from year to year in the seven-year Shemittah cycle; the point at which a budding fruit is considered to belong to the next year of the cycle is the 15th of Shevat.
We mark the day of Tu B'Shevat by eating fruit, particularly from the kinds that are singled out by the Torah in its praise of the bounty of the Holy Land: grapes, figs, pomegranates, olives and dates. On this day we remember Devarim "Deuteronomy" 20:19 and reflect on the lessons we can derive from our botanical analogue.
Devarim - Chapter 20
19. When you besiege a city for many days to wage war against it to capture it, you shall not destroy its trees by wielding an ax against them, for you may eat from them, but you shall not cut them down. Is the tree of the field a man, to go into the siege before you?