|Halacha of the day|
/ Many people attempt to eat on Tu Beshevat at least one fruit which requires a Shehecheyanu. When eating such a fruit, the Shehecheyanu should be said prior to reciting the Ho'eitz bracha. If he has already partaken of other fruits (at that particular sitting) than he only needs to say the Shehecheyanu upon eating the new fruit.
Many also have a custom of eating Bokser (carob) on this day. It is questionable whether one says a Shehecheyanu when eating bokser, since it is inedible when fresh. One must wait until it hardens a bit before it becomes edible and then the new bokser is not any more distinguishable from older stock and thus would be similar to nuts upon which no Shehecheyanu is said (see Sefer Bircas HaShir Vehashevach for further elaboration).
There is yet another custom which many have and that is to eat Esrog, either in the form of preserves, sugared slices, etc. It seems that the consensus of opinions is that no Shehecheyanu is said on the Esrog. One reason given is that the Shehecheyonu has already been said over the Esrog on the first day of Succos.(see Nitei Gavriel, Laws of Tu Beshevat 2:7)