In order for an image to be considered high contrast, it must contain striking opposition without much mid tone activity. A simple black and white photo cannot attain this without crisp whites, very dark blacks and virtually no grays. Not to say that this photo, if shot again, couldn't attain this goal. It would be quite simple. Make sure you have good lighting and be sure that your focus is tack sharp. This is blurred, so the eye is searching for a true point in which to rest. The composition is good. The single sunflower against the fencepost is good - as one is dead, the other is alive, one is truly natural, the other has been altered by man. Without the ability to use advanced editing techniques, it makes it harder to achieve some of the goals needed to really make a ribbon contender. But, with perfect focus and good positioning, you can work with brightness and contrast, to create a really effectively contrasting shot!!
i like the softness of the flower against the sharpness of the wood. i think it's a great contrast though most will probably be looking for the subject to be contrasty, not the overall pic, at which point you could be in trouble.
I like your idea for the challenge and the textures. I believe cropping more off the top would make for a stronger composition. And the flower definitely should have been sharper. If at all possible try to reshoot this. I think you've got a potentially great image here.
This is a good concept, the flower and the wood are a nice contrast to each other. As a black and white, though, IMO it lacks depth and is a little flat.
For me, I find your photo soft and of similar tones, not high contrast compared to other entries. I do like your composition and point of view though. :-)