- Peninei Halakha
During the omer period, one may buy a new fruit, garment, or piece of furniture and recite the berakha of She-heĥeyanu (the berakha recited over special occasions or new experiences) over it. However, in Ashkenazic communities, after the Crusades and the horrific massacres that the Christians carried out against Ashkenazic communities during the omer period, some rabbis began treating the mourning of the omer period as stringently as that of Three Weeks. According to this position, just as we refrain from reciting She-heĥeyanu during the Three Weeks – because it is inappropriate to recite, “Who has given us life…and brought us to this time,” during the period in which the Temple was destroyed – so too, it is inappropriate to recite She-heĥeyanu during a time in which holy Jews were murdered.
In practice, however, the accepted halakha is that there is no prohibition against reciting She-heĥeyanu during the omer period, because these days are not comparable to the days between 17 Tamuz and Tisha Be-Av. Nonetheless, one who wishes to be stringent and refrain from buying clothing and furniture during this period should be commended. In a time of need, however, even one who is generally stringent may be lenient. For example, one who needs an article of clothing or a piece of furniture may buy it. Similarly, if an opportunity arises to buy one of these items at a reduced price, he may buy it. Those who follow the more stringent custom should wear the garment for the first time, and recite She-heĥeyanu over it, on Shabbat, Rosh Ĥodesh, Yom Ha-atzma’ut, or at a se’udat mitzva. Likewise, if one buys a new piece of furniture, he should try to begin using it on one of these joyous days.
Similarly, one may buy a house and even move into it during the omer period, especially if the house is in Eretz Yisrael, and all the more so if it is located in an area that is devoid of Jews, because buying a house in such a place fulfills the mitzva of settling Eretz Yisrael optimally. An individual buyer recites She-heĥeyanu, and a married couple recites Ha-tov Ve-hametiv.
One may invite friends to a meal during the omer period, as long as they do not play musical instruments there. One may also go on a trip or go hiking, because one must avoid only joyous activities, not all pleasurable ones. Even though some are stringent in this regard, the halakha follows the more lenient opinion when it comes to these customs of mourning. Nevertheless, it is better not to schedule a school trip until after Lag Ba-omer, because such trips are very joyous. However, a school may schedule an educational trip during this period, even le-khatĥila.
 Leket Yosher quotes his teacher, R. Yisrael Isserlein, the author of Terumat Ha-deshen, as saying that one should avoid reciting She-heĥeyanu during the omer period. Several other Rishonim and Aĥaronim rule similarly. However, many Aĥaronim reject this stringent custom, including Ma’amar Mordechai 493:2 – quoted in mb 493:2 – and Kaf Ha-ĥayim 493:4. See Yabi’a Omer oĥ 3:26 and Yeĥaveh Da’at 1:24, which summarize the various opinions. Some are stringent regarding moving into a new house, because this is a very joyous occasion, similar to the joy of a wedding (Responsa Avnei Tzedek, yd 44). Yeĥaveh Da’at 3:30 rules leniently.
It is important to note that the omer period has a joyous side as well. Accordingly, Ramban writes (in his commentary on Parashat Emor) that they are like Ĥol Ha-mo’ed, like intermediate days between Pesaĥ and Shavu’ot. However, they also have an aspect of tension and suspense, since one must ascend during this period from one level to the next, until he reaches the pinnacle of the giving of the Torah at Sinai. When one is unable to climb from one level to the next in the proper order, the result is crisis and misfortune, as the Jewish people have experienced throughout their history. This is why we mourn during the omer period. Nevertheless, the holiness of these days remains intact, and thus this period is still very conducive to spiritual growth and purification, in anticipation of the giving of the Torah and the opportunity to attain intimacy with God.
 See the volume Bein Pesach LeShavu’ot 15:10, 12, which cites the more lenient opinions. Also see Hilchot Chag B’Chag 7:11, where the author leans toward being strict, but brings the lenient opinion in a footnote. See below, 8.6, regarding trips during the Three Weeks.