The Magen Avraham explains that even though Rosh Chodesh is referred to as a “mo'ed” (a festival), it is not a yom mishteh ve'simcha (a day of feasting and rejoicing). The Yad Ephraim points out that Purim is indeed referred to as “yom mishteh ve'simcha” (Megillat Esther 9:17), but he notes that Rosh Chodesh is de'oraita (Biblical) while Purim is not.
In reference to the Tachanun prayer and nefilat appayim (lit. falling on one's face during the act of prostration), the Mechaber states (Orach Chayyim 131:6) that the custom is not to do so on Tu B'Shevat and other semi-holidays. (Note: The Talmud in Megilla 22b refers to the custom of falling on the face when prostrating during the Tachanun prayer on a public fast day. Rav, who happened to be in a synagogue in Babylon on a public fast day, did not “fall on his face” when the rest of the congregation did so. The Gemara assumes that the reason was that the floor of the synagogue was made of stone, and we are taught in Vayyikra 26:1, “Ve'even maskit lo titnu be'artzechem le'hishtachavot ale'ha ? You shall not place a stone covering in your land to prostrate yourselves upon it.” “Ale'ha” is understood to refer to a stone covering “in your land,” meaning wherever you live, but not in the Temple, where it is permitted. The Gemara also offers an alternative answer ? that it is only full prostration with arms and legs extended that is prohibited everywhere but in the Beit Hamikdash. Therefore, today we make sure that there is something, such as the arm, that separates between the face and [any] floor.)
There is no mention of a formal seuda in regard to Tu B'Shevat, just as there is none for Rosh Chodesh. But the Magen Avraham and the Ba'er Heitev (loc. cit.) cite two interesting minhagim (customs). One is that on days when we do not say Tachanun, “Bnei Austria” (Jews living in Austria) did not eat lentils since these denote mourning. The other custom mentioned is that we, “Bnei Ashkenaz,” the Ashkenazic Jews, eat many kinds of fruits growing on trees. Of course, we have to be careful to recite the shehecheyanu blessing on new fruits in addition to the regular blessing we make before eating fruit (see Shevet Mussar quoting the testament of R. Eliezer Hagadol to his son).
Although “Bnei Ashkenaz” are mentioned specifically, the Sephardim also celebrate Tu B'Shevat. In fact, Rabbi Yitzhak Yosef, Rosh Kollel of Chazon Ovadyahu and son of the Gaon Rabbi Ovadya Yosef, devotes no less than nine paragraphs to the laws of Tu B'Shevat in his halachic book Yalkut Yosef. He notes (Hilchot Tu B'Shevat, Siman 4) the custom [of Sephardic Jews] to learn Mishna and Zohar on the night of Tu B'Shevat, including, of course, the laws pertaining to orla, Teruma (the first produce offered to the Kohanim), and tithes.
In Siman 6 he examines the situation when Tu B'Shevat occurs on the Sabbath, and the question when the new fruits are to be brought to say the shehecheyanu blessing over them. If the fruit is served after Kiddush, but before washing for the meal, there is a dispute among Poskim whether the Grace After Meals serves as a substitute for the Beracha Acharona, the blessing that is normally said after eating fruit, based on the principle “safek berachot lehakel,” namely, when there is a doubt about the requirement for a blessing we tend to be lenient. He expresses the opinion that it is therefore proper to serve the new fruits during the meal, before Birkat Hamazon, so that the fruits are definitely included in the Grace After Meals.
We have a glimpse of the importance of trees in our life when we read in Parashat Shoftim (Devarim 20;19) the admonition not to destroy fruit- bearing trees when we lay siege to a city. The phrase, “Ki ha'adam etz hasadeh” is taken to mean that we should not destroy trees because they do not attack us as people do, and also that man depends on the tree, “For man is the tree of the field.” All the commentators refer to man's dependence on the fruit of the tree for his sustenance. The tree is considered as a source of life and we are anxious to preserve it.
The Talmud (Ta'anit 7a) relates that when R. Zera was not feeling well enough to teach the Law, R. Jeremiah asked him to expound something of an aggadic character. He replied by quoting R. Yochanan on the verse, “But is man a tree of the field?” Since it states “from it you shall eat,” and “it you shall not destroy,” but it also states in the following verse, “It (an ornamental tree) you may destroy,” we derive from the wording that if a scholar (who is compared to a fruit-bearing tree) is worthy, we should eat (i.e., learn) from him.