Anyone who has been to an Israeli kindergarten or has heard songs taught there knows that Tu B’shvat is the time of year in which almond trees bloom. Although the Talmud connects this holiday (15th of Shvat, which falls on January 16 this year) with the new year for the trees, and gives the date significance in Jewish law relating to fruits and tithes, the connection to almond trees blooming is a more modern one.

My almond tree blooming, last year

My almond tree blooming, last year

This is the time of year that I am accustomed to seeing the blooming of my own almond tree in my back yard or other trees along my commute to work from the Shomron (Samaria) to Tel Aviv. But not this year; today is the day before Tu B’shvat and not a single tree in the area has bloomed yet. Why is that?

In order to answer this question, one has to understand the way trees determine when to bloom and the modern Jewish calendar. Trees are “programmed” to bloom in specific seasons. Trees need to bloom at specific times in order to ensure healthy fruit formation. A tree can sense the length of the day and can also “count” the number of cold days, and based on these “observations” the tree will bloom at the proper time.

The modern (Western, or Gregorian) calendar is arranged strictly according to the solar year. Each date on the solar calendar corresponds to a specific season, which corresponds to a specific position of Earth relative to the sun. The Jewish calendar is a calendar based on the sun and the moon. The months are lunar months which begin corresponding to the new moon.

A Jewish calendar month can be either 29 or 30 days, corresponding to the average time between two new moons (about 29.5 days.) A Jewish calendar year can be a “regular” year, made of 12 months and having a length of about 354 days, or a leap year, made of 13 months and having a length of about 384 days.

In order to keep the Jewish calendar in sync with the seasons so that the holidays fall out in the proper times, the modern Jewish calendar has a 19 year cycle, in which most years are regular years, but 7 years are leap years. During regular years, the Jewish calendar “lags behind” the Gregorian calendar, making the holidays occur earlier, because of the about 11 day difference in year length between the Gregorian and Jewish simple year length. The holidays are pushed forward during a leap year, having about 384 days, which is significantly longer than a Gregorian year.

Of the 19 year modern Jewish calendar cycle, a leap year occurs every two or three years. Years 3, 6, 8, 11, 14, 17 and 19 are leap years and the remainder are regular years. Today, we are in 5774, which is a leap year corresponding to year 17 of the 19 year cycle. We have not added a leap month yet; the leap month is always added next month, during the month of Adar.

Although leap years may occur every two to three years, During the last 9 years (from after year 8 of the cycle until this year, year 17) leap years have occurred only every three years. The practical outcome of this fact is that over the last 9 years, the Jewish calendar has been pushed ahead less (and as a result has lagged behind the Gregorian calendar more) than in any other 9 year period of the Jewish calendar cycle. As a result, the holidays this year occur earlier each season, relative to the solar year, than in any other year of the 19 year cycle.

This explains the lack of almond flowers this Tu B’shvat. An additional outcome of this is the fact that we just experienced the rare occurrence of Hanukkah falling out on Thanksgiving in November (Thanksgivukkah) rather than in late December or January.

Don’t worry, we are about to add a leap month in a few weeks and the holidays will return to their normal seasons. Rest assured that the almond trees will soon bloom, albeit after Tu B’shvat.