Last year's Tu B'Shevat post is here.
For biblical background, see here. The name "New Year for Trees" comes from Mishnah Rosh HaShanah 1.1. That passage gives two alternative dates for the celebration, one from Shammai and one from Hillel. Hillel's date (15 Shevat) is the one celebrated at present. The Hebrew phrase Tu B'Shevat means "the 15th of Shevat."
The first link above gives last year's date range for the holiday on the top right. Hopefully, this will be corrected by the time you see it.
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