The short answer to the question is: it depends. Some award winning images are entirely shot in camera, some are enhanced in the darkroom, some are enhanced digitally.

The ultimate question here is one of philosophy. Where does each individual person draw the line of what tools can be used and at what stage of the process before that individual will call it "editing"? Is it at the point of capture? Does it include basic techniques necessary to produce a print in a darkroom? Can you dodge and burn the image? Can you manipulate the contrast and color? Can you use a computer?

Every image has been "edited" even if you're only talking about adjusting the settings on the camera when capturing the image. The choice of lens, focal length, aperture, shutter speed, filters, even the type of film stock are all of artistic decisions in how to manipulate the light before and during capture. These, by extension, affect the nature and quality of the image. This is, by definition, editing the image. The only meaningful distinction is that it is pre-capture editing rather than post-capture.

Often, people think of editing as being something that is only done in a computer, but editing images after their capture is nothing new and has been part of photography from the very beginning. Adjusting exposure and contrast on the print, dodging, burning, tinting and adjusting the color are among the hundreds of analog editing techniques. Even the newest of these have existed for well over a century.

Even the greatest landscape photographers of all time would spend countless hours in the darkroom perfecting their images. Consider this quote from Ansel Adams:

The negative is the equivalent of the composer's score, and the print the performance.

This is why if you look at the rules of many photography competitions, they will include a declaration of how much editing is considered acceptable for that particular competition.

All that being said, generally speaking, a photographer's goal is to get the most perfect image they can in camera. Landscape photography in particular is often a game of patience. It is not uncommon for award winning landscape images to require a photographer to wait hours, days, even months to capture the perfect image.

Of course, as a general rule of thumb, the earlier in the process you edit the image, the better.