This year, 5777, Tu Bishvat will fall out this coming Shabbat. On such a year when Tu Bishvat falls out on Shabbat (and it is customary to eat a variety of fruits on the night of Tu Bishvat, as we have mentioned as well), the Poskim disagree whether the fruits should be eaten between Kiddush and the Hamotzi blessing, after the Hamotzi blessing has already been recited, or after Birkat Hamazon altogether.
Let us briefly discuss the various opinions:
The Opinion of the Razah
The Razah (acronym for Rabbeinu Zerachya Ha’Levi, commonly known as the “Ba’al Ha’Ma’or”) writes regarding the night of the Pesach Seder when the first two cups of wine are drunk before the Hamotzi blessing that an after-blessing should not be recited on the wine, for Birkat Hamazon exempts the after-blessing on the wine. The Rosh rules likewise.
The Opinion of the Rif
On the other hand, the Rif, Ramban, and others write that one should indeed recite an after-blessing on the wine before reciting the Hamotzi blessing, for wine that was drunk before Hamotzi cannot be exempted from its after-blessing with Birkat Hamazon.
The Ruling of Maran zt”l
Since there is a disagreement between the Rishonim regarding this matter, Maran Rabbeinu Ovadia Yosef zt”l writes that one should therefore preferably not enter this kind of doubtful situation and one should eat the fruits only after having recited the Hamotzi blessing and not beforehand. (See Responsa Yechave Da’at, Volume 1, Chapter 82, Chazon Ovadia-Yamim Nora’im, page 97, and Chazon Ovadia-Tu Bishvat and Berachot, page 4.) In this way, Birkat Hamazon will exempt the after blessings of the various fruits according to all opinions.
Serving the fruits after Birkat Hamazon
Maran Rabbeinu Ovadia Yosef zt”l writes (Chazon Ovadia-ibid, page 8) that the most preferable practice on the night of Tu Bishvat which coincides with Shabbat is to place the fruits on the table but to eat them only after Birkat Hamazon, for in this way, one will be able to recite both blessings before and after (“Al Ha’etz” and “Boreh Nefashot”) eating the fruits and vegetables, thus affording one the opportunity to recite more blessings on Shabbat and completing the daily quota of reciting one-hundred blessings.
Summary: It is preferable to serve the fruits on the night of Tu Bishvat which coincides with Shabbat only after Birkat Hamazon. One should not eat the fruits between Kiddush and the Hamotzi blessing.