It depends how heavy you are. It depends how fast you'll be riding on dirt and grass. It depends on the ruggedness of the surface you're riding on. It depends how frequently you'll be riding on it. It depends on the structural integrity of your particular frame and wheels. It depends on how much pressure you put in your tires. So in summary, it depends.
Road bikes are pretty tough, though. I've been riding for over 20 years and although I've broken a few wheels over that time, I've never broken a frame.