Why sunflowers/girasoles?

The original rape victim (ie. the one we see at the start of the film only) is found in a field of sunflowers if memory serves me correctly - so the night of the sunflowers could be about the night the rapist first struck.

Though I think the sunflowers are to be taken figuratively more than literally...
- Sunflowers have significant connotations with the sun, so 'night of the sunflowers' suggests a hidden world, one that isn't often considered.
- It could also be a reference to how sunflowers will turn away once you take the light off of them - a parallel to the reaction of the father figure/head policeman who turns away from the events and actions of his son in law

I'm not sure there really is an answer. I suspect it is intentional on the part of the director to have the audience debate this.

As already said, there was a scene at the very beginning where the rapist/murderer was walking away from a field of sunflowers.

"Girasol" means "sunflower", but literally means "turning-to-the-sun"; a sunflower orientates its "head" to the sun and turns along with the movement of the sun during the day (in order to catch as much light as it can). "La noche de los girasoles", literally Night Of The Sunflowers, is referring to the fact that during the night, the sunflowers don't have the sun to orientate themselves towards, so the flowers could be facing in any direction. The characters in this movie are like sunflowers during the night; they are caught in a situation/environment where the "moral light" to guide them is absent so to speak, and hence they are prone to making bad choices and falling into evil behavior/acts.

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