The 15th day of the Hebrew month of Shevat, known as Tu b'Shevat, is the New Year for Trees.
Why do trees celebrate their New Year so much later than ours? It has to do with the rainy season in Israel, which starts on the festival of Sukkot. It takes four months for the rains to saturate the soil, nurture the trees and coax them into producing fruit. This is important to know if you are planning to give your tithes (different charities and gifts) of fruits, as we did in Temple times, because the required tithes changed from year to year.
We humans can also celebrate along with the trees. After all, the Torah says, "Man is a tree of the field." We are nurtured by deep roots, as far back as Abraham and Sarah; we reach upwards to the heavens while standing firmly on the ground; and when we do all this right, we produce fruits that benefit the world—namely our good deeds.
Eat some fruit on this day. Best if you can get some of those fruits for which Israel is famous: olives, dates, grapes, figs and pomegranates.
The blessing on fruit:
Baruch Atah A-donay, Elo-heinu Melech ha'Olam borei pri ha-etz.
[Blessed are You, L-rd our G‑d, King of the universe, who creates the fruit of the tree.]
If tasting a fruit for the first time in its season, recite the Shehecheyanu blessing before saying the fruit blessing:
Ba-ruch A-tah Ado-nai E-lo-he-nu Me-lech ha-olam she-heche-ya-nu ve-ki-yi-ma-nu ve-higi-a-nu liz-man ha-zeh.
[Blessed are You, L-rd our G‑d, King of the universe, who has granted us life, sustained us, and enabled us to reach this occasion.
Some also have the custom to eat carobs on Tu B'Shevat.