The Custom of Eating Fruit on Tu Bishvat

[Shut She’eilat Shlomo vol. 1 #212]
Question: There are those who say that we are obligated to eat fifteen different fruits on Tu Bishvat, since Tu Bishvat is on the fifteenth day of the month of Shevat. Is this a custom or a law?
Answer: There is no mention in the Mishnah or Talmud that Tu Bishvat is a day of joy, rather it is the new year for trees. This means that it is the date that differentiates between the fruit of the past year and the coming year in terms of the obligation to tithe the produce (Rosh Hashanah 15). Among the Rishonim (Earlier Authorities), Tu Bishvat is mentioned as a day on which Tachanun is not recited (Minhagei Maharil), and this is the ruling of the Shulchan Aruch (Orach Chaim 131:6). The Magen Avraham mentioned the Ashkenazic custom to enjoy many fruits (brought in the Mishnah Berurah ibid. #31), and this is also the Sephardic custom (Pri Eitz Hadar – seder limud le-leil Tu Bishvat). The quantity of fifteen fruits, however, is not mentioned. Our master, Rav Avraham Yitzchak Ha-Cohain Kook, wrote, "As is customary, there is on it [Tu Bishvat] an impression of a festive day, the first indication of the revival of the settlement in our Holy Land (Igrot Ha-Re’eiyah vol. 2, p. 61). It says in the Jerusalem Talmud (end of Kiddushin), "Rav Bon said: In the future a person will have to give an accounting for all that his eyes beheld, but he did not eat." Rav Bon’s intention was not that a person should be a glutton and eat everything in his sight; rather he should endeavor to taste everything (obviously everything that is permissible) at least once. And it also relates that Rabbi Eleazar was concerned about this idea, and he would save his money in order to eat each of the year’s new produce. Similarly, the Mishnah Berurah (Orach Chaim 225:19) writes, "It is meritorious to eat a little from each year’s new produce. The reason is in order to demonstrate the preciousness of Hashem’s creation." He does not mention, however, that one must eat fifteen types of fruit.
Summary: It is an ancient custom to enjoy many fruits on Tu Bishvat. And it is praiseworthy to eat fruits which one does not normally eat during the year.