ShalomNewYork.com

“The 15th day of the Jewish month of Shevat is the official “birthday” for trees in Israel. Calculating the years of a tree is necessary for several mitzvot of the Torah: ma’asorot - tithing [of each year’s fruit]; orla-forbidden fruit of a tree’s first three years; reva’i-[redemption of] the fruit of a tree’s fourth year; shemita-the Sabbatical year. Tu B’Shevat is considered the beginning of the year for trees because it is the mid-point of winter: the strength of the cold becomes less, the majority of the year’s rains (in Israel) have fallen, and the sap of the trees starts to rise. As a result, fruit begins to form. (Fruit that was already ripe is known to have been nurtured by the previous year’s rain.)” more@KabbalaOnline.org