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Which Trees Suit the Bracha Requirements?
- It is permissible to make a Bracha on a tree that was planted or guarded during Shemitta year. 
- It is permissible to make a Bracha on a tree that is within 3 years of being planted even though it is considered Orlah. 
- One should not make the Bracha on a tree which was made from grafting two species, however, there is what to rely on to make the Bracha. 
- One should only make the Bracha on a fruit tree and not a barren tree. However, if one made a Bracha on a barren tree one shouldn't make another Bracha upon seeing a free bearing tree.
- It is questionable whether one may make a Bracha on a fruit tree which did not produce fruit the year one makes the Bracha. 
Text of Bracha
- The text of Birchat Ilanot is ברוך אתה ה׳ אלוקינו מלך העולם שלא חיסר בעולמו כלום וברא בו בריות טובות ואילנות טובות ליהנות בהם בני אדם. 
Who is obligated?
- Men are obligated to recite the Birchat Ilanot. However, the obligation to recite such a bracha is only if you see the trees flowering should you recite the bracha but not that you have to go and find them. However, it is a pious practice to do so.
- Although there is a discussion if women are obligated since it could theoretically be considered a time-bound mitzvah, nonetheless, the poskim hold that women may recite Birchat Ilanot. 
- It is preferable to say the Birchat Ilanot in Nissan, however, if one has not yet made the Bracha, it is permissible to make it even after Nissan, and after the fact one may also recite the Bracha before Nissan.  Nonetheless, in places that the trees bud in Adar one may make the bracha in Adar. 
- Preferably, one should say Birchat Ilanot the first time one sees a budding tree in Nissan, however, if one did not one may still recite Birchat Ilanot even if one previously saw a budding tree and did not make the Bracha the first time. 
- The Bracha is recited when the tree starts to bloom, meaning carry flowers, leaves are not enough. 
- If the tree's buds matured into fruits one may no longer make the Bracha. However if some of the fruit begin to grow and some flowers and buds remain one may still say the Bracha. 
- One may say Birchat Ilanot even on Shabbat, yet it is preferable to make it during the week if it does not result in one missing out on making the Bracha altogether. 
- One may say Birchat Ilanot even at night if there is enough light for one to distinguish between trees that are blooming and ones that are not. 
- In Australia trees bud in Elul and Tishrei one should therefore say Birchat Ilanot in those months rather than in Nissan.
- It is preferable to gather a minyan (10 people) in order to make the Bracha of Birchat Ilanot. 
- It is better for one person to say the Bracha out loud and everyone else to say it quietly to themselves. 
- A blind person cannot make Birchat Ilanot, however, it is proper to listen to the Shaliach Tzibbur make the Bracha. 
- One may make the Bracha even if one sees the tree through glasses(including sunglasses).
- Preferably the Bracha should be recited on trees located outside of the city. 
How many trees are needed to be able to make Birchat Ilanot?
- Some poskim hold that one should only make the Bracha upon seeing two fruit trees.  However, many poskim hold that one may make the Bracha even on one tree. 
- It's sufficient to have two trees of the same type but it is preferable to have at least two different types of trees. 
- Tur and Shulchan Aruch 226:1. Rambam Brachot 10:13, Gemara Brachot 43b, Kitzur Shulchan Aruch 60:1
- Halichot Shlomo (vol 1, 2:4)
- Chazon Ovadyah (Pesach pg 19), Dovev Meisharim 3:5, and Chelkat Yaakov 2:27 (2:56). Divrei Malkiel 3:2 rules that if one is sure that it is an orlah tree then he shouldn't say the Bracha on it.
- Chazon Ovadyah (Pesach pg 15), Nitei Gavriel (Pesach 6:13). Yabia Omer 5:20, Sdei Chemed Brachot 2:7, Minchat Yitzchak 3:25:3, and Ben Ish Chai Parashat Reeh halacha 11 all say that its preferable not too as well.
- Kitzur Shulchan Aruch 60:1, Mishna Brurah 226:2, Halachot Ketanot 2:28
- Chazon Ovadyah (Pesach pg 13), Shevet Halevi 6:53. Lehorot Natan 5:8 writes that there's no proof that really one can't recite the bracha upon a nice barren tree but nonetheless the halacha follows the Mishna Brurah.
- Mishnat Yosef 1:60 writes that even if in that year it does not carry fruit but it is however a fruit tree one may make the Bracha. However, LeHorot Natan 5:8 and Maaseh Chemed (2 note 64) disagree. Chemdat Avraham 2:10 says it is not lechatchila but if there is no other tree you can make the Bracha.
- Shulchan Aruch 226:1. See further: Text of Brachot#Birchat Ilanot.
- Shulchan Aruch 226:1, Gemara Berachot 43b
- Teshuvot Vehanhagot 1:190
- Yalkut Yosef (Kitzur Shulchan Aruch 226:2), Chazon Ovadyah (Pesach pg 10), Nitei Gavriel (Pesach 7:6), Har Tzvi 1:118, Tzitz Eliezer 12:25, Teshuvot Vehanhagot 1:190.
- The Gemara Brachot 43b writes that one who sees the budding of trees in Nissan should make the Birchat Ilanot. Many Rishonim (including the Ritva Rosh Hashana 11a, Sefer Eshkol pg 68) comment that this Bracha is commonly made in Nissan but does not necessarily have to be made then. This is also the opinion of the Mishna Brurah 226:1 which states that the Bracha may be made in months other than Nissan. Rav Ovadyah Yosef in Sh"t Yechave Daat 1:1 and Chazon Ovadyah (pg 25) argue that it should be made starting in Nissan (and not Adar to be strict and take into account the opinions of the Halachot Ketanot 2:28 and Chida in Birkei Yosef 226:2) and if one has not yet seen a tree in bloom, one should still say it in Iyar. Sedei Chemed Berachot 2:1 and Kaf Hachayim 126:1 both rule that one should not say the Bracha before or after nissan. Nitei Gavriel (Pesach 6:2) writes that it should be said in Nissan.
- Chazon Ovadyah (pg 28), Mishna Brurah 226:1, Aruch Hashulchan 226:1.
- Halichot Shlomo (vol 1, 2:5), Chazon Ovadyah (Pesach pg 24), Nitei Gavriel (Pesach 6:9)Machatzit Hashekel 226, Shaar Hatziyun 226:3 and Badei Hashulchan 46:18. Kitzur Shulchan Aruch 60:1 and Kaf Hachaim 226:9 state that if one failed to say the Bracha upon seeing it for the first time one may no longer say the Bracha.
- Mishna Brurah 226:2
- Chazon Ovadyah (Pesach pg 26-7). This is also implied by Mishna Brurah 226:4.
- Chazon Ovadyah (Pesach pg 20), Nitei Gavriel (Pesach 6:9). Kaf Hachayim 226:4 quotes the Moed likol chai that the Bracha should not be said on Shabbat or Yom Tov because we are worried that one may come to shake or break a branch. He adds that according to Kabbalah the Bracha should not be said on Shabbat or Yom Tov. Rav Ovadia Yosef in Yechave Daat 1:2 writes that preferably one should not say it on Shabbat unless it is the last day of nissan and one still has not yet recited the Bracha.
- Chazon Ovadyah (Pesach pg 11), Tzitz Eliezer 12:20(6)
- Nitei Gavriel (Pesach 6:17)
- Chazon Ovadyah (Pesach pg 12), Nitei Gavriel (Pesach 6:14)
- Chazon Ovadyah (Pesach pg 12)
- Chazon Ovadyah (Pesach pg 28)
- Chazon Ovadyah (Pesach pg 29)
- Chazon Ovadia page 8, Kaf Hachayim 226:3 quoting Lev Chayim 45.
- Chazon Ovadyah (Pesach pg 13-5 note 9), Sh"t Tzitz Eliezer 12:20(6). Halachot Ketanot 2:28 writes that one can only recite the bracha when seeing two trees.
- Nitei Gavriel (Pesach 6:11) writes that according to the strict law one may make Birchat Ilanot on one tree. Betzel Chachma 6:36:6, Kaf Hachaim 226:2, and Teshuvot Vihanhagot 1:191 agree. Rav Yitzchak Yosef (Motzei Shabbat Vayhakel Pekudei 5778 min 18-25 explained that the strict law is that one can recite the birchat ilanot on one tree and if it will cause bitul torah or the like one may recite the bracha on one tree.
- Chazon Ovadyah (Pesach pg 14), Halachot Ketanot 2:28. Kaf Hachayim 226:2 says also that it does not need to be 2 separate types.