Since When Is March 20 The First Day Of Spring?

Still half asleep, I hear the morning news show on TV blabbering about the first day of Spring.
Man, how long have I been asleep? I went to bed on March 19, and I always thought the various equinoxes start on the 21st. What up? Is it because it's leap year? Some crazy math thing? I guess the planet knows it's Spring, even if the calendar says otherwise.