Cycles of 91 (45.5 days)

B"H

On Tu B'Shvat, we celebrate the Rosh Hashanah L'Ilanot (New Year of the Trees).  It's brought down in many sources that Ilan is gematria 91, which equals the gematria of the name Hashem (26) + the name Adni (65).

91 x 4 = 364, which is the same as 52 x 7, the cycles most explored in our book.

There is a custom on Tu B'Shvat to drink four cups of wine, just as in the Seder, representing the four seasons (white and red wine are mixed to represent those seasons).

Tu B'Shvat this year falls on day 137 of this year. 136.5 is 91 x 1.5, or 45.5 x 3. Tu B'Shvat falls half way into the second season (winter), 4.5 months into the semester (or year).

There appears to also be a rough parallel with the life of the Lubavitcher Rebbe. The Rebbe was born on 1902. He passed away at 92, after having had his first stroke two years earlier, as he was close to completing 91 years of age. He became Rebbe on the 10th of Shvat.