Rosh Chodesh Nisan marks the start of the season for saying Birkat Ha-Ilanot, the bracha said upon seeing fruit trees in bloom (as stated in Brachot 43b). This is one of only 4 brachot said by all Jews just once each year! The Bracha: B.A.A.E.M.H. shelo chaser b'olamo klum, u'bara vo briyut tovot v'ilanot tovim, layhanot bahem bnei adam (Blessed is G-d; nothing is missing from His world; He created good things such as trees, so that Man might benefit from them). Ideally, we say this bracha when first seeing fruit-bearing trees flowering in Nisan; but the bracha may still be said for as long as the fruit has not yet ripened. A "hidur (enhanced) Mitzva" is to say the bracha on 2 or more trees together, with a minyan. But a single person may also say it, on a single tree. Women should also recite this bracha, which can be said either day or night, weekday or Shabbat/Chag. Many have the Minhag to say the bracha on the 1st day of Chol HaMoed Pesach.