I have done many, many flower images. Usually, I photoshop the background out because I feel it detracts from the pure beauty of God's creation. It takes anywhere from one to three hours to eliminate the background. The time depends on how much contrast there is and the complexity of the flower edge, I never cut the flower; the images are all obtained in situ. Most of the images were taken in my backyard.
The color I use for the background is usually obtained from the center of the flower or is a complementary color. Frequently, I use a dark red background that I have fallen in love with. In my opinion, it works great with a large number of flowers.