I spent a good part of New Year's Day at the Planting Fields Arboretum photographing Orchids. Since there were no crowds, I was able to use my tripod, and take time to set things up right. For the background, I simply used a black t-shirt. My wife was kind enough to hold it behind the flowers for me, so she gets partial photo credits on these.
Camera settings: Canon 100mm macro, f11, 1/15th.
Below, I've included an example of how a simple black background can have a dramatic impact on a still life subject. On the left, the greenhouse door is clearly visible, and quite distracting. On the right, the black t-shirt proves to be a very effective solution.
A few things to mention. If these flowers were in the wild, I would ALWAYS opt to utilize their natural surroundings. However, when you are in an area where the man made elements make it impossible to find a clean background, you need to improvise. Also, I know a good number of photographers who could likely duplicate the black background using Photoshop. Personally, I find that technique to be way too time consuming. I feel it is always better to get the shot right IN the camera, rather than in the digital darkroom later.