Why do some hospitals ban cut flowers?

Flowers seem like the perfect gift when someone is sick, but some hospitals don't allow them, especially around cardiac and intensive-care units. More than likely, this is because studies show that the water in a vase of cut flowers can carry infectious-disease bacteria. No one has become sick from this, however. There also is a longstanding belief that flowers suck up oxygen, which would be bad for an ailing person. In truth, flowers and other plants emit 10 times more oxygen than they use. So a hospital room with flowers will be more oxygenated than one without flowers.