The prevalent custom among Ashkenazi Jews today in Eretz Yisrael combines several traditions. Most expressions of mourning last until Lag B’Omer, while some continue afterwards. This is based on the tradition that although the plague ended on Lag B’Omer, those students who fell ill beforehand died between the 34th day of the Omer and Shavu’ot (Maharal, Chidushei Aggadot, Yevamot 62b). Therefore, [Ashkenazim] do not take haircuts, celebrate weddings, play music, or dance until Lag B’Omer. Afterwards, however, they refrain only from weddings and very joyous affairs. Another reason: during the Crusades and the [Chmielnicki] Massacres of 5408-5409 (1648-49), hundreds of thousands of Ashkenazi Jews were killed, and these murders occurred mainly during the latter part of the Omer period. Therefore, Ashkenazi communities refrain from great celebrations during this period. From Rosh Chodesh Sivan, however, the custom is to permit weddings, because the holiday of Shavu’ot, which is already perceivable from the beginning of the month, cancels the mourning. Some rule leniently and allow weddings from Lag B’Omer and on, avoiding only great celebrations that are optional in nature until Shavu’ot. (In the footnote, we will mention another custom that was very widespread in Ashkenazi lands.) died until P’ros HaAtzeret to mean approximately half-a-month [before Shavu’ot]. Furthermore, according to this custom, there is no great difference between the Ashkenazi and Sefardi customs. Nonetheless, we still continue to avoid great celebrations even after Lag B’Omer, in accordance with the tradition that claims that R. Akiva’s students who fell ill before the thirty-third died throughout [the remainder of] the Omer period. Furthermore, the Taz writes (493:2) that it is because of the tragedies that occurred after Lag B’Omer. Another explanation for this custom: it coincides with our version of the Gemara (Yevamot 62b), which states that they died between Pesach and Atzeret (Shavu’ot). And since refraining from getting married is the [only] expression of mourning mentioned in the works of the Ga’onim, we do not celebrate weddings during the entire [Omer] period (except from Rosh Chodesh Sivan and on, that being the only detail in which this custom deviates from the Gemara). The prohibition against taking haircuts and listening to music was instituted later; therefore, the custom is to refrain from them only until Lag B’Omer. Another way to interpret the Ashkenazi custom is that thirty-three days of mourning are required, [not necessarily the first thirty-three]. Accordingly, we count thirty-three days starting from the day after isru-chag until the 29th of Iyar (not including Rosh Chodesh Iyar and Lag B’Omer). Everything is, thus, permissible from Rosh Chodesh Sivan and on. Some [authorities] permit weddings after Lag B’Omer, if necessary, because they fulfill a mitzvah, forbidding only great celebrations that are optional in nature, until Shavu’ot.
In Germany, the Jews adopted the fourth custom mentioned above, according to which the important thing is to observe thirty-three days of mourning at the beginning or end of the Omer period. Here, too, there are several options: 1) at the beginning of the Omer (like the Ashkenazi custom in Eretz Yisrael); 2) from the thirtieth of Nissan, which is the first day of Rosh Chodesh Iyar, until the morning of the third of Sivan; 3) from the second of Iyar until the day before Shavu’ot (Rama 493:3, M.B. 15; also see Hilchot Chag BeChag 7, 73-75).
The Rama (493:3) writes that a community should not follow two different practices, because of [the prohibition of] Do not divide yourselves (Devarim 14:1). However, if people from different communities assemble together in one place, they may [follow different customs]. [R. Moshe Feinstein] concurs in Iggrot Moshe, O.C. 1:159. According to Ashkenazi practice (the fourth custom mentioned in section 2), if there is no established custom in a particular city, the residents may chose one of the customs, as long as they do not adopt the leniencies of both. They may even observe the first thirty-three days one year and begin on Rosh Chodesh Iyar the next, because these are not [really] different customs, the important thing being to observe thirty-three consecutive days of mourning. This is taken from [Responsa] Chatam Sofer (O.C. 142), as Iggrot Moshe (O.C. 1:159) explains it. It is also quoted in Siddur Pesach KeHilchato 12:4:23 and Hilchot Chag BeChag 7:23. See also Piskei Teshuvot 493:12-13. The Chatam Sofer writes further that one may follow one practice regarding weddings and another regarding haircuts. Nowadays, there are practically no Ashkenazim in Israel who [begin the mourning period on Rosh Chodesh Iyar and thus] celebrate weddings [in between Pesach and] Rosh Chodesh Iyar. It seems appropriate to stop those who want to make weddings then, because the Israeli practice is also based on the third custom mentioned above (sec. 2), and one should not follow two practices in one place. ]
On the day of Lag B’Omer itself, one may get married and take a haircut. There is a dispute, however, regarding the night. Some say that these actions are permissible at night, as well, because the entire day of Lag B’Omer is joyous. Others maintain that one is required to observe thirty-three consecutive days of mourning. Therefore, it is permissible to get married and take a haircut only after morning has arrived and we can apply the rule: “Part of a day is [considered] like a whole day.” The custom is to act strictly, le-chatchillah (ideally), but one may follow those who rule leniently, if necessary. According to all customs, it is permissible to celebrate with music and dancing on the night of Lag B’Omer. is permissible. They include the authors of Ma’adanei Yom Tov, Chok Ya’akov, Mor U’Ketzi’a, and more. Their reasoning is that Lag B’Omer, both night and day, is a time of joy, when [R. Akiva’s students] stopped dying. The problem, however, is that we need to observe thirty-three days of mourning. According to those who do not celebrate weddings until Rosh Chodesh Sivan, these is no problem, because [they observe] more than thirty-three days. There is also no difficulty according to our version of the Maharil, which states that one must avoid haircuts only thirty-two days (although he writes that we refrain from weddings the entire Omer period). The author of Shulchan Aruch HaRav (493:5) makes this halachah contingent upon the question of whether or not we recite tachanun in the Minchah service before Lag B’Omer. I.e., according to those who hold that tachanun is omitted, the mourning period lasts thirty-two days, and the custom is to omit tachanun (see below, chap. 5, note 1). If we, nonetheless, insist on thirty-three days of mourning, and we do not count the days after Lag B’Omer, perhaps we can rely on the Ramban’s opinion that a portion of the night is tantamount to an entire day. Then, we can celebrate weddings and take haircuts a few moments after the night of Lag B’Omer begins (so writes the Pri Chadash). See Hilchot Chag BeChag 7:71, who substantiates this opinion. See also Siddur Pesach KeHilchato 12:12. ]