I was told that this year since Sukkos falls on Shabbos, we are therefore lenient in various laws of the Daled Minim, including that this year we do not have to be careful that the middle leaf, known as the Tiyomes, be completely closed on its top. Is this correct? And if so, why is this the case?
While certainly leniency’s do apply this year, nevertheless, this mainly applies in Israel and not to the Diaspora. Furthermore, even in Israel, one can argue that it is initially proper to be stringent to the same level of Hiddur that is followed by a normal year. Accordingly, even in Israel, and certainly in the Diaspora, one should try to purchase a Lulav with a completely closed middle leaf as done in other years, although certainly one who does not do so has upon what to rely even if he normally does so by other years, and even in the Diaspora. Furthermore, especially in Israel, if a completely closed middle leaf Lulav is difficult to find, or is too expensive, one may even initially purchase a Lulav with a not completely closed middle leaf.
Explanation: It is true that in years that Sukkos falls on Shabbos certain leniencies are applicable towards the validity of the Daled Minim [being that this year the shaking of Lulav is only rabbinical as we do not shake the Lulav on Shabbos which is the only biblical day of obligation]. However, this mainly applies in Israel, where the first time that the Daled Minim are shaken is on the first day of Chol Hamoed, which receives a pure rabbinical status of a mitzvah, and hence the validity of the Daled Minim in Israel in such years follows the more lenient rabbinical criteria of validity applicable for Chol Hamoed. However, in the Diaspora, where the Daled Minim are shaken on the second day of Yom Tov, we initially follow all of the biblical criteria of validity applicable to the first day of Sukkos, and hence in essence when purchasing a set of Daled Minim in the Diaspora even in such years, one should initially purchase a set of the same level Hiddur as he would do in any year.
Now to tackle your specific question regarding a split in the middle leaf: On the first day of Sukkos the Lulav must contain at least a partially attached middle leaf in order for it to be valid, and it is a Hiddur for this middle leaf to be completely closed from top to bottom without any split. However, on Chol Hamoed, the Lulav remains valid even if it’s middle leaf is completely split and certainly if it is only partially split. Accordingly, in Israel this year seemingly one may be lenient to even initially purchase a Lulav that contains a split middle leaf, even though in normal years he would be particular for the middle leaf to be completely closed. However, in the Diaspora, it would remain proper for one to be stringent even this year to purchase a Lulav which contains a completely closed middle leaf, even though from the letter of the law this is not necessary even in a normal year and certainly this year when the mitzvah is only rabbinical. Certainly, in the Diaspora one may not initially purchase a Lulav that contains a completely split middle leaf, which is initially invalid on the second day of Yom Tov. Furthermore, one can argue that even in Israel, it is proper to initially purchase a Lulav with a completely attached middle leaf as done in other years, and certainly that one should not purchase a Lulav with a completely split middle leaf, as although it is certainly valid for the mitzvah in such years, nonetheless, the Achronim conclude that it is proper to initially be stringent even on Chol Hamoed regarding the Chaser invalidation’s of an Esrog as it is not proper to use a blemished item for a mitzvah, even if it is Halachically valid and perhaps we can apply the same also to the Lulav that it is not proper to initially use a Lulav with a split middle leaf which is invalid due to Chaser. Furthermore, if one travels to the Diaspora for the holiday and is taking his Daled Minim with him, he would need to purchase a set that is initially valid for the Diaspora. The same applies if he plans on shaking the Daled Minim in the old city of Jerusalem, which according to many has a biblical status.
Sources: See regarding the validation leniencies applicable to Chol Hamoed: Admur 649:17-19; Rama 649:5; Tur 649; Rosh 3:3; Tosafos Sukkos 29b; Biur Halacha 648 “Shinuiy”; Chaim Ubracha 197; See regarding the status of the second of Yom Tov in the Diaspora: Admur 649: 17 and 18; 21 See regarding that even on Chol Hamoed the Esrog should initially not contain a Chaser invalidation: Toras Chesed O.C. 36; Meiri Sukkah 36b [It’s a Midas Chassidus to bless over a whole Esrog even on Chol Hamoed]; Raavad in Tamim Deim 233; Bikureiy Yaakov 649:39; Kaf Hachaim 649:76 [it is possible that based on Kabbalah the Esrog should be whole even on Chol Hamoed]; Mikraeiy Kodesh 2:26; Piskeiy Teshuvos 648:4; 17; See regarding the middle leaf being completely closed: Admur 645:10; Rama 645:3 in name of Yeish Mefarshim and that so is custom; Rashi Sukkah ibid “And the spine split until the lower leaves”; Tosafos Sukkah 32b; Terumos Hadeshen 96; Or Zarua 2:306