"For the Lord your G-d brings you to a good land... a land of wheat, barley, grape, fig, and pomegranate..."
(Devarim 8:7)

The 15th day of the month of Shevat commemorates the beginning of the "new year" for trees. Tu B'Shevat marks a new year for calculating the age each tree for purposes of tithing. In the Torah, fruit from trees grown in the land of Israel are prohibited from being eaten during the first three years. Fruit that grows in the fourth year is for the Lord. From the fifth year on, the fruit can be eaten.

In Israel today, it is a tradition to plant new trees, as well as partake of all of the fruits of the land to mark the joyous day, and to remember that trees are an asset and a blessing.