Seek And Destroy
I have a quiz for you: What mitzvah do you do just once a year but do not say shehechianu? Well, one answer is destroying our chametz (leavened food) the day before Pesach. My question is: Why don't we say shehechianu on the mitzvah of destroying our chametz?
Good question. Shehechianu is the blessing we say upon experiencing the joy of reaching a new season in life. For example, we say shehechianu when eating a new fruit, putting on a brand-new suit, and when doing a mitzvah that comes around once a year.
So why don't we say shehechianu on the once-a-year mitzvah of destroying our chametz? Because, although we feel the joy of performing a mitzvah, we are also aware of the fact that we are engaged in an act of destruction.
Another explanation is simply that there is no need to say shehechianu at the time of destroying our chametz, because we rely on the shehechianu blessing that we say at the Pesach Seder.
- Ta'amei Haminhagim 487-8