- The name Isru Chag derives from the verse “Isru Chag Baavosim Ad Karnei Hamizbeiach.” This means to say that this day is to be attached [i.e. Isru] to the Holiday itself, and by doing so the verse considers him to have built an Altar and sacrificed on it an offering. The Arizal taught that on the day after Yom Tov, Isru Chag, a ray of the Holiday still shines. For this reason, the following customs are relevant on Isru Chag: One is to increase a little in eating and drinking on Isru Chag. Even a Chasan and Kallah on the day of their wedding may not fast on this day. Similarly, a child may not fast on his parent‘s Yahrzeit.
- Some Poskim write that the customs of Isru Chag [increasing in food and drink] apply also to the night after, which is Motzei Isru Chag.
- Some Poskim rule that one is to wear Shabbos clothing on Isru Chag.
- Tachanun is omitted from Davening from Erev Yom Kippur until the beginning of the month of Cheshvan. The prayer of Tzidkascha is not recited on the Shabbos between Erev Yom Kippur and the month of Cheshvan.
- When does one begin to say it? Mashiv Haruach Umorid Hageshem is recited beginning from Musaf of Shemini Atzeres. On Shemini Atzeres prior to the silent Musaf prayer, the Chazan announces Mashiv Haruach Umorid Hageshem. It is then recited in the Musaf prayer and every prayer thereafter.
- Until when is it to be said? Mashiv Haruach Umorid Hageshem is recited until, but not including, Musaf of the 1st day of Pesach. Those who Daven the Nussach of Arizal/Sephard, omit Mashiv Haruach and begin reciting Morid Hatal from the silent prayer of Musaf of the 1st day of Pesach. The Chazan thus announces prior to the silent prayer of Musaf “Morid Hatal.” Those however who follow Nussach Ashkenaz still say Mashiv Haruach Umorid Hageshem by the silent Musaf of Pesach and only begin to omit it with the repetition of the Chazan of Musaf and all prayers thereafter.
- If one forgot to say Mashiv Haruach-Nussach Sephard/Arizal: Those who Daven Nussach Arizal or Nussach Sephard and recite Morid Hatal in the summer months, fulfill their obligation if they accidently said Morid Hatal instead of Mashiv Haruach. Even if one remembered prior to finishing the blessing of Mechayeh Meisim, he is not required to go back and recite Mashiv Haruach.
- If one forgot to say Mashiv Haruach-Nussach Ashkenaz: Those who Daven Nussach Ashkenaz and do not recite Morid Hatal in the summer months, do not fulfill their obligation if they omitted Mashiv Haruach. If they already concluded the blessing and began saying the next blessing [even the first word of “Ata”] they must return to the beginning of the prayer, irrelevant to where in the prayer they remembered of their omission. Similarly, if they remembered only after concluding the entire prayer, they must repeat the Davening. If one remembers prior to saying Hashem’s name in the blessing of Mechayeh Meisim, then he is to say it in the place that he remembers and continue from where he left off. [If he already said Hashem’s name then he is to finish the blessing and say it prior to beginning the words of the blessing of Ata Kadosh. The same applies] if he only remembered after concluding the blessing of Mechayeh Meisim but before beginning the next blessing [even the first word of Ata], then he is to say it there. If, however, he already began even the first word of the next blessing he must return to the beginning of the prayer, as explained above.
- If one is in doubt if he said Mashiv Haruach-Nussach Ashkenaz: Those who Daven Nussach Arizal or Sephard and recite Morid Hatal during the summer, are never required to go back even if they certainly did not say Mashiv Haruach, and certainly if it is a mere doubt. However, those who Daven Nussach Ashkenaz and are in doubt if they mentioned Mashiv Haruach are to consider it as if they omitted it, if this doubt occurred within the first 30 days after Shemini Atzeres [until 22/23 Kisleiv], and hence follow the same ruling as one who omitted it.
- When does one begin saying Vesein Tal Umatar? Those who live in Eretz Yisrael begin saying Vesein Tal Umatar Levracha starting from Maariv of the 7th of MarCheshvan. Those living in the Diaspora begin saying Vesein Tal Umatar on the 60th day past the beginning of Tekufas Tishrei. [Practically, it is to be said from the night before the 5th of December, and in years with 29 days in February, then the year before, it is said from the night before the 6th of December.]
- If one said it prior/post its allowed time-Eretz Yisrael: If one said Vesein Tal Umatar Levracha during the summer, outside of its allowed time, which is between Pesach and 7th Cheshvan [in Eretz Yisrael] or 5th December [in the Diaspora], there is a difference in law between Eretz Yisrael and the Diaspora. In Eretz Yisrael, if one said Vesein Tal Umatar after Pesach, [during the summer, which is any time between Chol Hamoed Pesach and the 7th of MarCheshvan], one is required to go back and repeat from the beginning of Bareich Aleinu. If one already concluded Shemoneh Esrei, then he must repeat it from the beginning.
- If one said it prior/post its allowed time-Diaspora: In the Diaspora, if one said Vesein Tal Umatar after Pesach, [during the summer, which is any time between Chol Hamoed Pesach and Shemini Atzeres], then if one is in a country that as a whole does not need rain during the summer, it follows the same ruling as Eretz Yisrael, and one must go back to Bareich Aleinu or repeat Shemoneh Esrei. If, however, one’s country as a whole requires rain even during the summer months, then one who said Vesein Tal Umatar during those months is not required to go back and repeat from the beginning of Bareich Aleinu. Nevertheless, if one wills, he may repeat the Shemoneh Esrei as a Tefillas Nedava.
- If one asked for rain after Sukkos, prior to the 7th of MarCheshvan, according to Admur and other Poskim, Shemoneh Esrei is to be repeated.
- In those countries [that in general need rain after Sukkos and that’s when their rain season begins], if one said Vesein Tal Umatar after the 7th of Cheshvan, prior to the 5th of December, he is not required to go back, or repeat Shemoneh Esrei. [This applies even if his country is not currently in need of rain, such as it already rained plenty, so long as it is a general time that the country needs rain. If, however, the country is not yet in need of rain, then Shemoneh Esrei is to be repeated if rain was mentioned prior to the 5th of December.] Nevertheless, if one wills he may repeat the Shemoneh Esrei as a Tefillas Nedava.
- One is to take down the Sukkah [immediately] after Sukkos in order to show that the Sukkas construction was purely for the sake of the Mitzvah. One is not required to bury the wood used for Sechach and it may be used and benefited from for any purpose that one desires. Nevertheless, it is proper to beware not to use it for a belittling matter, as this is disrespectful to the Mitzvah that was performed with it. It goes without saying that one may not trample on the Sechach in order not to do a belittling act with it. It is proper to save the Sechach to reuse the same Sechach for the following year’s Sukkah in order to reuse it for a Mitzvah purpose. If one does not desire to save the Sechach he may throw it in the garbage. However, it is proper not to place it together with all the other garbage and it is rather to be placed in a separate pile. Likewise, it is not to be discarded in an area that people walk and will trample over it. [Some have the custom to burn the Sechach used for the Sukkah in order not to use it for any other matter. This is a mere stringency.]
- It is proper not to perform a belittling matter even with the walls of the Sukkah. They are hence not to be thrown directly into the garbage. It is permitted to use them for a non-belittling use.
- It is debated amongst the Poskim as to whether the floor of the Sukkah may be used for a belittling matter during the year.
- On Motzei Yom Tov, one is to take the Lulav together with the other species and place it in a special area for safekeeping. One is to place it within view as through seeing it and remembering the Mitzvah one will merit to be saved from any suffering or stress. One should not take the Daled Minim and throw them in the garbage being that they hint to a very holy and sublime matter. [Many are accustomed to save the Daled Minim until Pesach in which they are then burned together with the Chametz.]
- If one does not desire to save the Daled Minim he may throw it in the garbage. However, they are to be placed in a separate bag and only then to be placed in the garbage.
- Hadassim for Havdalah: It is proper to use the Hadassim used during Sukkos for the Mitzvah of Besamim by Havdalah, in order to add another mitzvah to its use. One is to use it together and in addition to a spice which its blessing is Borei Minei Besamim, such as clove and cinnamon. [The above, however, is not the widespread custom and many save or simply discard the Hadassim.]
- Aravos to bake the Matzos: Some have the custom to save the Aravos of the Lulav to use as fuel for baking the Matzos.
- Esrog jelly: Some are accustomed to make Esrog jelly from the Esrog of the Daled Minim. The jelly is consumed on the night of the 15th of Shevat which is the Rosh Hashanah for trees. The consumption of this Esrog jelly is a Segula for women to have an easy birth. [Some are accustomed to also save the Esrog jelly to be eaten on Shavuos.]
- The Aravos for Hoshanos: Some have the custom to save the Aravos which were hit on Hoshanah Raba and use them as fuel to burn the Chametz on Erev Pesach. [Others are accustomed to throw the Aravos on top of the Aron. Others negate this custom. The Rebbe was not accustomed to throw the Aravos on top of the Aron. Others are particular to save the Aravos as a good omen and Segula as explained next. Based on this it is proper not to burn all the Aravos on Erev Pesach in order so some are saved for the Segula.] The Aravos are a Segula for safety during travel, for being saved in a time of danger, and for being saved from fear and frightening dreams. Some write that cooking the Aravos and drinking the water is a Segula for having children.
What is one to do with the Kedushas Shevi’is Esrog after Sukkos?
One must guard the Esrog and may not discard it until it has spoiled and is no longer edible.
Esrog Jam: It is permitted to make Esrog jam with an Esrog of Kedushas Shevi’is.
Besamim: It is unclear if one may enter cloves into the Esrog and use it as Besamim.
- The Rebbe Rayatz stated in the name of the Alter Rebbe and in name of the Baal Shem Tov that Shabbos Bereishis, which is the first Shabbos of the year which follows the holiday season, has ability to effect one’s entire year. In his words “The way one stands on Shabbos Bereishis, so is drawn onto the entire year.” On this Shabbos there is a light of Chochmah which shines and this light extends to every day of the year, and all its important events, general and personal, including: Shabbos, Yomim Tovim, Hachnasas Lecheder, Bar Mitzvah’s, etc. All these events receive from the light of Shabbos Bereishis. The decrees that were written on Rosh Hashanah, sealed on Yom Kippur, and packaged on Hoshanah Raba, do not leave for shipment until Shabbos Bereishis.
- On Motzei Shabbos Bereishis we pronounce “Yaakov Halacha Ledarko,” that Yaakov Avinu has begun his journey.
- Some Chassidic communities are accustomed to leave the white Paroches on the Aron and Bima until after Simchas Torah, and some leave it until after Shabbos Bereishis.
- Some are careful to avoid saying Kiddush during the 7th sixty-minute hour past the average midday and so is the Chabad custom. In New York this is between 6:00-7:00 pm throughout the year, except for when DST is active in which case it is between 7:00-8:00. In Eretz Yisrael, this is between 5:40-6:40 pm throughout the year except for when DST is active in which case it is between 6:40-7:40. Some Rabbanim however rule one is to always avoid Kiddush from 6:00-7:00 in all places. One is to recite Kiddush either prior to this time, or afterwards. Initially one is to recite Kiddush immediately upon returning from Shul and hence if he arrives home before the start of this time he should hurry and make Kiddush beforehand.
- Those who are careful to avoid Kiddush during the 7th hour avoid it with all forms of wine, irrelevant of color.
 The reason: As this is considered Derech Achilaso.