Tashlich on Shmini Atzeret
Can one say Tashlich until Shmini Atzeret?
The custom is to say Tashlich after Mincha of the first day of Rosh Hashana (Rema Orach Chaim end of 583 and Mishna Berura ibid:8).However, if one didn’t manage to say Tashlich on Rosh Hashana he can say it throughout the Ten Days of Repentance. Some have the custom to always recite Tashlich during the Ten Days of Repentance on the day of the “13 Attributes” — the day before Yom Kippur eve. (See what the Munkaczer rebbe writes in his book Sha’ar Yissochor, Maamor Shuva Yisroel #22-23 and Responsa Divrei Yisroel 1:167).