The Mystery of Tu Bi-Shvat

Tu Bi-Shvat is a bit of a mystery to me. The entire concept of a new year for trees that is fixed on the lunar calendar is difficult for me to understand. The Mishnah (Rosh Hashanah 2a) states that the 1st of Shevat is the new year for trees according to Beis Shammai, and according to Beis Hillel it is the 15th (t"u) of Shevat. We follow Beis Hillel, which means that, for example, fruits that are gathered from a tree before Tu Bi-Shvat cannot be grouped together with fruits that are gathered from a tree after Tu Bi-Shvat for the purposes of terumos because they are from different years (Shulchan Arukh, Yoreh De'ah 331:57,125).

But why should Tu Bi-Shvat be the dividing line between years?

Click here to read moreBut why should Tu Bi-Shvat be the dividing line between years? The Gemara (Rosh Hashanah 14a) answers that most of the rainy season is over by Tu Bi-Shvat. Tosafos (ad loc., sv. be-echad) explain that this is when the fruits ripen from the rain from the current year (meaning, since Rosh Hashanah in Tishrei). In other words, it is an issue of seasons.

However, this is somewhat difficult because the seasons are determined by the solar calendar (cf. Rashi, Sanhedrin 12b sv. be-chushbena). If the new year for trees is a matter of seasons, then shouldn't it be determined by the solar calendar? Shouldn't it be X number of days after the winter solstice? Instead, the way it currently is, it drifts based on the Jewish luni-solar calendar so that this year it fell out on Feb. 9th, last year on Jan. 22nd, the year before on Feb. 13th, and the prior year on Jan. 25th. That is a swing of over 3 weeks!

The Gemara (Rosh Hashanah 15a) recognizes this issue and asks whether Tu Bi-Shvat is determined based on the lunar or solar calendars, and it answers that it is based on the solar. But it does not offer a reason. Tosafos (ad loc., sv. de-chadashim) offers two reasons why it is based on the lunar calendar:

1. The moon also affects the fruit cycle (cf. Deut. 33:14).
2. The Jewish people follow a (mostly) lunar calendar.

This second answer is expanded upon by R. Shlomo Goren in his Toras Ha-Mo'adim (5756 edition, pp. 242-243) based on a passage in the Talmud Yerushalmi (Rosh Hashanah 1:2). The Yerushalmi asks why the new year for the jubilee is on the first of Tishrei and not the tenth, since the Torah specifically associates the tenth of Tishrei with the jubilee (Lev. 25:9). It answers that we want all months in a year to be the same (approximate) length and if we have a new year beginning on the tenth of a month, it splits a month into two odd lengths in different years. The Yerushalmi then points out that Tu Bi-Shvat, the new year for trees, is in the middle of a month but offers no response.

R. Goren suggests that, for ease of counting, we have all new years begin on the first day of the month. Tu Bi-Shvat is an exception but it is in exactly the middle of a month. If we had a new year anywhere else in a month, it would cause great confusion for those attempting to determine the age of various items. If we were to have a new year for trees that drifted among the lunar months, there would be great confusion in, for example, the determination of which fruits can be combined for terumos and ma'aseros. Therefore, since we generally count according to the lunar calendar, the new year for trees was fixed according to it also even though the precise phenomenon might be different by a few days (or weeks).