This year Rosh Chodesh Nissan occurs on Shabbat. When should we bless Birkat Ha'Ilanot? on Shabbat or on sunday? Can we make the blessing on Motze'ey Shabbat?

Thank you for your question: On the one hand there is an advantage in saying the bracha on Shabbat because of the basic halachic rule of ‘zrizim makdimim’ (diligent people are quick to do a mitzvah) On the other hand ,there is a minority of poskim who hold that one should not say this blessing on Shabbat. Regarding saying the bracha at night-- there is a dispute if one may say the bracha at night. Therefore, if someone wants to say the bracha right away to be zrizim makdimim that’s certainly fine but I would recommend waiting until Sunday morning and thereby one can fulfill the bracha according to all the poskim. Details: Bracha on shabbat: Some poskim wrote that the bracha should not be said on Shabbat for two different reasons: 1. There is a suspicion ׂ(חשש) that someone who says the bracha on Shabbat might come to pick off the flowers from the tree (Kaf Hachaim 226:4). 2. According to the kabbalah, when someone makes the bracha he is taking the holy sparks out of the non-kedusha and consequently it is like he is doing the prohibtion of ‘borer’ (selecting) on Shabbat (Ben Ish Chai and Kaf Hachaim). Harav Ovadia Yosef (Chazon Ovadia, Birkat Hailanot 5) disagreed with these claims and claimed that the fear that a flower could be pulled off was not mentioned by Chazal and we can't make up new suspicions. Additionally, we don’t even have to touch the tree when we say the bracha, so why should we be worried that someone will pull of a flower? Regarding the second reason, Harav Ovadia explained that there is no prohibition of ‘borer’ by a spiritual type of selection, and we should not mix kaballa and halacha. In the book Nefesh David (siman 19) the Aderet (Harav Kook's father-in-law) wrote that he would always say the bracha on Shabbat purposely because on Shabbat our shmone esre has less brachot than on the weekdays and we are lacking a few brachot to reach 100 brachot. Therefore, he would say the bracha to help him reach the number of 100 brachot on shabbat. Harav Ovadia concluded that it’s permitted to say the bracha on shabbat but why not stay on the safe side according to all the poskim and therefore it’s better to say it on a weekday. However, at the end of a long footnote in the Chazon Ovadia, Harav Ovadia commented that when Rosh Chodesh fell on Shabbat he ruled that we should, in fact, say the bracha on Shabbat since it is the first day to say the bracha. see also shut minchat asher (part 3, 14;5). Bracha at night: Harav Ovadia Yosef wrote (Chazon Ovadia, Birkat Ha'iIanot 1) that there is no problem saying the bracha at night if one can see the trees with an electric light. He quoted the Tzitz Eliezer and Shut Yayin Hatov who also hold that there is no problem saying the bracha at night. However, other poskim disagree because in the day the flowers bloom and one can enjoy their beauty better. The Gemara says that one should say the bracha in the days of the month of Nissan. This could be understood to mean that only in the days and not in the night should one say the bracha (see Har Tvi, 1:118 or L'tzion 118, Chemday Tzvi 1:18). After all of this discussion there are three options. The first option is to say the bracha on Shabbat Rosh Chodesh-- going with the priciple of zrizim makdimim (and helping us achieve 100 brachot on shabbat). Option two is if someone doesn’t want to say the bracha on Shabbat; according to the Ben Ish Chai and Kaf Hachaim, he can hurry up and say the bracha on motzaei Shabbat according to the poskim who hold that one can say the bracha at night. Option three is to wait till Sunday morning and say the bracha in a way that all the poskim hold that is fine. See Minchat Asher Beraisit, siman 22 who discusses similar questions of conflicts between zrizut and hidur mitzvot. I personally think that the best way is to wait until Sunday to play it safe, but if someone wants to say it on Shabbat that is definitely fine too. All the best