Full moon falls this upcoming weekend, and with it comes the holiday of Tu BiShvat, the Jewish New Year of the Trees.

My only experiences with Tu BiShvat growing up were of faithfully bringing a five-dollar bill to school to pay for the planting of a tree in Israel. Each tree could be bought in honor of someone. I was more interested in deciding whose name would go on the JNF certificate than in the actuality of the trees so many thousands of miles away. Once I left the Jewish Day School, I basically forgot about Tu BiShvat for twenty years. Deciding to play with the holiday as an adult meant beginning, as usual for me, with research.

It turns out that the Jewish year has four different New Years. Tractate Rosh Hashanah of the Talmud tells us, "On the first of Nisan is the new year for kings and for festivals. On the first of Elul is the new year for the tithe of animals. ...On the first of Tishrei is the New Year for the years.... On the first of Shevat is the New Year for the tree according to the school of Shammai; the school of Hillel says on the 15th." Since modern-day Judaism follows Hillel in most things, the new year of the trees is celebrated on the 15th of Shvat, at the full moon in the middle of the month.

Originally, the day was used for calculating the age of trees for tithing. According to the Torah, trees grown in the land of Israel may not be eaten from during their first three years; the fruit of their fourth year must be tithed to God; after that, the trees can be harvested at will. To make accounting simpler, Tu BiShvat became the birthday of every Israeli tree; regardless of when a tree was planted, its birthdays were marked on the full moon at the middle of the month of Shvat.

In the sixteenth century, the disciples of Rabbi Isaac Luria developed an elaborate Tu BiShvat seder, in which thirty different fruits were consumed in an allegorical journey through four mystical worlds of creation, from the physical world of embodiment to the essential world of pure spirit.

Some Jews regard Tu BiShvat is a kind of hinge-point within the year, between the season of darkness (Chanukah) and the season of light (Passover). Some conceptualize the round of the Jewish year as a single long day, in which case Tu BiShvat comes around 3 a.m., an hour which is neither precisely night nor precisely morning.

Trees are a potent symbol within Judaism. In Genesis, Adam and Eve get themselves exiled from Eden by eating the fruit of the wrong tree. According to the Zohar, that tree (the Tree of Knowledge of Good and Evil) was merely a branch of the Tree of Life until the first humans ate the forbidden fruit, at which point the branch split off and became a tree unto itself. In this teaching, tikkun olam (the healing of the world) means re-unifying the two trees into their initial, singular, state. In Deuteronomy, man is likened to a tree; in Proverbs, the Torah is likened to a tree of life. The Kabbalists of medieval years had a variety of ways of conceptualizing God, including the "sefirotic tree," an arboreal diagram of divine spheres through which holy emanations flowed into creation.

In the last thirty years, as the crisis of the global environment has become clear, many Tu BiShvat observences have come to have a strong environmentalist component. It's traditional to plant trees in the Land of Israel, which connects the holiday to the greening of that particular desert. Some conceptualize the holiday in a more local or global way, as a kind of "Jewish Earth Day," in the parlance of the Coalition on the Environment and Jewish Life.

Tu BiShvat has become one of my favorite minor festivals. I like the custom of leading a seder in which different fruits and wines are consumed to represent a journey through the four worlds. It's a wonderfully strange holiday, and I'm glad I gave it a second chance in adulthood; planting imaginary trees in a faraway land in second grade didn't begin to scratch the surface of how cool this holiday can be.

In an alternate interpretation, suggested by a modern scholar of comparative religion, this weekend is not Tu BiShvat but rather Tuba Shabbat, when Jews worldwide bring our large brass instruments to shul to have them blessed before we use them to accompany the melodies of the morning service. I don't know about you, but I think a brass quintet in shul would be a lot of fun...