The Gemara comments that a person who sees the blossoming of trees during the month of Nissan recites Birkat Ha’ilanot (the Beracha giving praise to God for fruit trees). The Ritba (Rabbi Yom Tob Ben Abraham of Seville, Spain, 1250-1330), in his commentary to the Gemara (Rosh Hashanah 11), writes that this Halacha does not apply only in the month of Nissan. Whenever a person sees the new blossoming of trees, he recites the Beracha. According to this view, then, the annual recitation of Birkat Ha’ilanot may be done anytime one sees blossoming trees, even if this happens before or after the month of Nissan. This is also the position of the Seda La’derech (Rabbi Menahem Ben Aharon, 14th century). The Roke’ah (Rabbi Elazar of Worms, 12th-13th century) also followed this view, explicitly interpreting the Gemara as specifying Nissan only as a common example, but not to the exclusion of other times. This is also the opinion of the Mahasit Ha’shekel (Rabbi Shemuel Halevi Kelin, Germany, 1724-1806), in Siman 226.

Others, however, disagree, noting that according to Kabbalistic teaching, Birkat Ha’ilanot should be recited specifically during the month of Nissan. This is the view of the Ben Ish Hai (Rav Yosef Haim of Baghdad, 1833-1909) and of Rav Haim Palachi (Turkey, 1788-1869), in his work Mo’ed Le’chol Hai (1:9).

Hacham Ovadia Yosef, in his work Hazon Ovadia, rules that one should satisfy all opinions and recite Birkat Ha’ilanot specifically during the month of Nissan. Nevertheless, if one did recite the Beracha earlier, upon seeing blossoming trees during Adar, he has fulfilled his obligation. Similarly, if one was unable to recite the Beracha during Nissan, he may still recite the Beracha when he sees blossoming trees during Iyar, relying on those authorities who maintain that the Beracha does not have to be recited specifically during Nissan. Furthermore, in geographic locations where trees blossom during a different time of year, such as in areas in the southern hemisphere, where blossoming occurs around the time of Tishri or Heshvan, one recites the Beracha when seeing blossoming trees in that season.

In New York, however, one should certainly try to recite the Beracha during the month of Nissan.

Summary: One should recite Birkat Ha’ilanot upon seeing blossoming trees during the month of Nissan. If one mistakenly recited the Beracha upon seeing blossoming trees during the month of Adar, he has fulfilled the Misva. One who did not recite the Beracha during Nissan may recite it upon seeing blossoming trees even after Nissan. People in geographic locations where blossoming occurs around the time of Tishri or Heshvan recite the Beracha when seeing blossoming trees in that season.