Like Tim, its not something I have done, but you will certainly benefit from a seamless background (a large sheet of paper, clamped at the top, down onto the table) would be much better.
Do you get to choose the vase? If it must be "on-show" in the photo, I think you it would look better with an opaque one rather than transparent - as my eyes are drawn to the stalks rather than flower heads, but preferably I wouldn't show it, or only show the top couple of inches.
Your lighting also needs a little attention, the yellow flower on the left has blown highlights, the others look a tad dull - although that could be the flowers colouring.
What lights are you using? If you have two, maybe set both at the same level, or if not, try adjusting using a reflector (which can be another piece of white paper) on camera right.
Getting closer, I think, will improve things considerably.
TJ