Someone made the blessing on blossom in the Northern hemisphere in Nissan and then went to live in the Southern hemisphere (where it is possible to make the blessing in Elul (see here ). Do the sources explain whether and why he can make the blessing in the Southern hemisphere?
The Shulchan Aruch (OC 226) writes that a person should only recite this blessing once annually ("ואינו מברך אלא פעם אחת בכל שנה ושנה"). Accordingly, Rabbi Eliyahu Cohen (Ma'aseh Chemed 1:20, see also note 47) writes that, although a person in the Southern Hemisphere should recite the blessing when most trees blossom in that part of the world, this does not apply to someone who had already recited the blessing in the month of Nisan in the Northern Hemisphere ("כל זה לבני המקום אבל מי שבירך בניסן בארץ ישראל לא יברך שוב בתשרי במדינות הדרום שהרי אין לברך אלא פעם אחת בשנה"). He also postulates that this might not apply in the reverse, as the new year starts with Nisan.
On the other hand, he suggests that the seasons in each hemisphere might be treated as entirely independent and therefore require their own blessings. As a result, he suggests that a person who travels to a different hemisphere can fulfill their obligation out of doubt by hearing another person's blessing.