Daf Yomi - Sukkah 39 - Story Regarding Brochos

The Sefer Bais Shearim records an incident regarding a person who walked into Shul while the Congregation was reciting Hallel. The man took out his lulav and joined them in the recital of Hallel. After he finished reciting Hallel, he realized that he had forgotten to recite the blessing on the lulav. The Bais Shearim ruled that he could no longer recite the blessing because he had forfeited the essential aspect of the mitzvah, which is to take the lulav bundle and wave it during the recital of Hallel, and the blessing on the mitzvah can only be recited prior to or during the performance of the mitzvah and not afterwards. The Bikkurei Yaakov, however, disagreed, and he maintained that since it is our custom to recite Hoshanos while still holding the lulav, it was deemed as if he was still in the midst of performing the mitzvah, thus allowing him to recite the blessing.