I hate selective coloring 99% of the time....but we all go through that phase I think. Almost always, it looks better if you desaturate the background some instead of completely. Leaving the background in color, but with less saturation will make the flower pop against the background while not giving it a cheesy photoshopped look.
Secondly, you need to think about being more creative with your composition. More often than not, a photo with the subject placed smack dab in the middle is less appealing than other possible compositions. I don't always stick to the rule of thirds, but I usually only break it if there is a valid reason in the image....which I don't see here.