Tu B’Shevat (15th of Shevat) is the Rosh Hashanah for trees, as it is the time when they are infused with sap and their fruits begin the earliest stage of development.
Tu B’Shevat is one of the dates used to calculate the years for Orlah (the first three years of a tree’s growth – when its fruit is forbidden), Revai (the fourth year of a tree’s growth – when its fruit must be consecrated), Terumah and Maaser (the tithes given to the Kohen and the Levi).
Outside of Eretz Yisroel, the laws of Orlah apply to any fruits known to have grown during a tree’s first three years, and the laws of Revai apply to grapes known to have grown during a vine’s fourth year. A Rav should be consulted to compute these times properly.
Even though Tu B’Shevat is the time of a fruit’s development in the Northern Hemisphere, it is still the date used when calculating Orlah and Revai for fruits grown in the Southern Hemisphere.
Contrary to popular misconception, Tu B’Shevat is not the day of judgement for trees. Rather, that occurs on Shavuos.
