When one sees blossoming trees for the first time one should say the following blessing: בָּרוּךְ אַתָּה ה’ אֱ-לֹהֵינוּ מֶלֶךְ הָעוֹלָם שֶׁלֹּא חִסַּר בְּעוֹלָמוֹ כְּלוּם וּבָרָא בוֹ בְּרִיּוֹת טוֹבוֹת וְאִילָנוֹת טוֹבוֹת לֵהָנוֹת בָּהֶם בְּנֵי אָדָם. (Blessed are You, L‑rd our G‑d, King of the universe, Who has made nothing lacking in His world, and created in it goodly creatures and goodly trees to give mankind pleasure.)
The blessing can only be said on a tree that has edible fruit. If one did not say the blessing the first time they saw such a tree they could say it as long as the tree did not start to produce its fruit. Preferably the blessing should be said on two or more trees.