landscape - Are three different exposures enough for a good HDR image?

I am a newbie to photography and shoot with Canon 550D ( Rebel T2i ) that can take 3 bracketed shots at a time. I want to know whether 3 shots are typically enough to capture the different lightings in the scene. I know that a lot depends on the particular scene I am shooting, but is it possible to know a generic answer for landscapes like beaches, sunset etc? I ask this cos I get to go to scenic places infrequently and its very difficult to experiment and learn there. If 3 are not enough, I can change the exposures manually and take a few more shots.