Before fulfilling the Misva of Lulav on the first day of Succot, two Berachot are recited. First, "Al Netilat Lulav" is said on the actual performance of the act. Second, "She’he’hiyanu" is recited for fulfilling the Misva in its set yearly time.
What is the Halacha if someone forgot to say "She’he’hiyanu" before taking the Lulav? If he is still involved in shaking the Lulav and the Hosha’anot, he may still recite "She’he’hiyanu." However, if he didn’t remember to recite the Beracha until after he completed the Misva, there is a disagreement between the Poskim whether he may recite it when taking the Lulav the next day. The Mishna Berura (Rav Yisrael Meir Kagan of Radin, 1839-1933) in his Sha’are Sion (662) ruled in the name of the Peri Megadim that he may not recite it, since he has already fulfilled the Misva for the first time on the previous day.
However the majority opinion of the Magen Avraham (662:1), the Levush 644:1, the Hayeh Adam (148:10) as well as Rabbi Moshe Halevy in his Birkat Hashem (Vol. 4, p. 108) holds that one may recite the "She’he’hiyanu" the next day, or any other day that he remembers, until Hosha’ana Rabba, the last day we take the Lulav.
SUMMARY
If one forgot to say She’he’hiyanu before shaking the Lulav on the first day, he may recite it before shaking the Lulav on the subsequent day that he remembers.
