Do you use a photo-editing programme? I think you should try to brighten the pictures a bit, and edit out the black in the background. I also agree with TheBathFactory, the green ones don't stand out against the glass.
Maybe you can try hanging them on a branch outside, if that's possible: The background would be blurrier because it's more distant, plus it might also be darker. Of course, then you might want to do this for all of them. In that case, perhaps just a different colour dish?
I don't know how I feel about them against the centre of the dish either. It might be that it's too close to the texture of the dish, I'm not really sure....
On the other hand, you have decent lighting (great white balance!) and nice, clear, clean shots, which is a lot better than many I've seen (some, I admit, I might've put up myself). Overall, I think you have the hang of it, and it'sjust small tweaks here and there (like brightening them).