Historical Background
Tu BiShvat began as a legal date rather than a major religious festival.
The Mishnah lists several different "new years" used for different purposes. One was the new year for trees. The fifteenth of Shevat eventually became the accepted date.
After the destruction of the Temple, many of the agricultural rules connected with Temple offerings no longer functioned in the same way. Tu BiShvat could easily have disappeared from Jewish life.
Instead, the day gradually acquired new meanings.
Jewish mystics living in the land of Israel gave Tu BiShvat special attention. A ritual meal developed in which fruits were eaten and passages from Jewish Scripture and tradition were studied.
In modern times, Tu BiShvat became strongly connected with the land of Israel. Tree planting became a popular custom. More recently, many Jewish communities have also used the day to think about care for the environment.