Since the days of Nissan are over can you still say the bracha for blooming trees with Hashem’s name after Lag Baomer?
Is it better to wait until Shabbath to recite it?
Is it better to recite it with a minyan?
Should one say it and have in mind all, as we do in kiddush?

A. On question 288 we wrote; This year, due to the earliness of Pesach, the blooming of trees at this latitude occurred very late on the Jewish calendar. Although “the days of Nisan” are mentioned in regards to reciting birchas hoilonos (Brochos 43b ”“ Shulchan Oruch O.H. 226, 1), Poiskim maintain that when required it could be said earlier on Adar (Kerem Shlomo 226,1 ”“ Shulchan Hatohor ibid. ”“ Bais Hayotzer 12 et al.) or after Nisan. (Chasam Sofer , hagoos O.H. 226 ”“ Zichron Yehuda ”“ Magid Taaluma 43b ”“ Nitey Gavriel, Pesach I, 6, 5) and even on Sivan (Aruch Hashulchan ibid. ”“ Nitey Gavriel ibid, see also question 83 on this forum).
In regards to waiting until Shabbos on question 287 we wrote; Yalkut Yosef (Shabbos 3, 319,77) quotes some opinions that maintain that this brocho should not be recited on Shabbos either because by engaging one’s attention on the tree one might come to collect some fruit (Moed L’kol Chai 9), or by dint of a cabalistic injunction on gathering “nitzoitzois” (spiritual sparks) from a tree on Shabbos (Kaf Hachaim 226, 4). However most Poiskim disagree and permit reciting this brocho on Shabbos. (Yalkut Yosef ibid. ”“ Nitey Gavriel, Pesach I, 6,7).
Horav Shlomo Miller’s Shlit”a opinion is that you can wait until Shabbos (avoid contemplating the tree) and recite together with a larger group “b’rov am” and have it adjoined to the count of the hundred brochos.
The Rov maintains that no minyan is required for reciting this brocho. However, since we always maintain that “Berov Am Haddras Melreh” or we honor of the King, when many are present, it would be preferred to have others join.
The Rov maintains that each one should recite his own brocho.

Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit’a