A spontaneous pot of petunias is about the same probability (within an acceptable margin of error) as life appearing (in the vastness of the universe multiple times). So, if we state that one can happen, we have to admit we also believe the other is likely. Are we happy to make that conclusion?
The chances of life appearing in the vastness of the universe *once* have to be as close to zero as makes no odds. The fact that life *does* exist (at least, I damn well hope so) surely means that the odds of it appearing again are significantly enhanced. Ergo, a bowl of petunias must have (by that logic) a much enhanced probability of springing into existence.