Tu B’Shevat has both simple and deeper understandings.
The simple explanation is “ראש השנה לאילנות” -The New Year for trees. Some people think it’s the trees’ birthday, some plant trees on this day…etc.
Simply said, just as we have a fiscal year in America, where donations given in one year can’t be applied to the next year, the same can be said for the trees. The apples that were grown last year, and the apples that will be grown this year are from two separate “fiscal’ years. So, when separating the 10%, you must use the apples from the correct fiscal year. Tu B’Shevat is the cut off. Anything that budded before Tu B’Shevat is considered from the previous year. Any new buds that grew following Tu B’Shevat are from the next year. That is the simple explanation of Rosh Hashanah L’Ilanot.
It’s customary to eat fruit on Tu B’Shevat and many have the custom to eat from the sheva minim. There’s also an interesting Syrian Tu B’Shevat custom to read a midrash written in Arabic by Rav Saadia HaGaon, that talks about the Aseret Hadibrot. (This can be found in the red pizmon book on page 515 targum aseret Hadibrot). On a simple level, Tu B’Shevat comes right before Parashat Yitro so it’s read at that time (although not a popular custom any more, men used to crowd the shuls to vie for a chance to bid on this Aliyah)
Tu B’Shevat is also the time to pray for an etrog, according to the Ben Ish Chai.
But there’s a question: It’s cold and wintery outside in most places. Why are we praying and talking about the tree when the trees have no buds and are totally bare?
The Gemara tells us that the luscious watermelon, peaches and plums we enjoy in summertime come from the rain in the winter. That means the rain, the minerals and the nutrients from the tree that will only start budding fully in Nissan, are going up the tree now, although we don’t see this. Our Hachamim and Hashem, however, look at the tree and say,”I see here, the fruit of the tree “… איזה הוא חכם, הרואה את הנולד”
Whom is a wise man ? one that can (look at a pregnant woman and ) see a baby. One can look at the tree and see the fruits that are coming.
Nissan is Spring. The fruits aren’t ready, they’re still budding. On Shavuot, we bring Bikkurim when the fruit is fully ready. And that goes on until Succot. This agricultural cycle is starting now. It’s the beginning of the cycle. In the winter it just rains- we aren’t really doing anything. We plowed after Succot, planted and seeded and now we wait for things to happen. Now, as the agricultural cycle is beginning, the sap is rising up the tree and the fruits are getting ready. That’s Tu B’Shevat.
There are spiritual implications as well. אדם עץ השדה- Man is compared to a tree.
We become a nation on Pesach. The sap of Pesach, so to speak, is going up the tree now. We might be spiritually desolate, with nothing going on. But Pesach brings rejuvenation, it’s the time when we become a free nation- and it’s starting now.
Therefore, I’d like to suggest a deeper reason for the Syrian custom of reading the 10 Commandments in Arabic on Tu B’Shevat. Those commandments are the minerals, the sap, that are going up the tree, preparing us. Emunah and Bitachon are our nutrients and our minerals, and the first one is: אנכי ה׳ אלוקיך I am Hashem Your G-d
That’s the beginning of the 10 Commandments and that’s everything! Rav Saadia HaGaon says all 613 mitzvot are found in the 10 Commandments, and all 10 Commandments can be found in the first pasuk, and the whole first pasuk is in the first word- Anochi- that’s the whole story.
You must know there’s a G-d out there that says I am here! That’s everything- it’s the whole religion on one foot and therefore, if we’re going to start our spiritual assent, it starts with that statement, of Anochi- I am Hashem your G-d.