On its face, the oxygen-depletion myth appears to have some backing. It's true that while plants typically absorb carbon dioxide and emit oxygen, that process changes at night. At night, plants absorb more oxygen than they produce, and they emit carbon dioxide.
So, flowers are bad, right?
In fact, flowers add far more oxygen to a hospital room than they use. In daytime, plants emit 10 times more oxygen than they use up at night, so a hospital room with flowers in it will actually end up more oxygenated than one without [source: Snopes]. And a study published in the journal International Archives of Occupational and Environmental Health in 1977 showed that even at night, plants only altered oxygen and CO2 levels in hospital wards by about 1.5 percent -- a negligible amount, in terms of air composition [source: Gale].
It's especially negligible when you consider that a human being, such as the sick person lying in the bed in the hospital room, uses up about 2.5 cubic feet (71 liters) of oxygen in an hour, while a pound of foliage sucks up about 0.026 gallons (0.1 liters) in that same time period. It would make far more sense to ban oxygen-sucking visitors than to ban flowers.
So why would a hospital ban flowers from intensive care units? Some people think the myth is simply so pervasive, hospitals have incorporated it in their policies. But more likely, it has to do with a potentially real health hazard associated with cut flowers: bacteria. Studies have shown that the water in a vase of cut flowers can carry harmful bacteria -- the kind of stuff that can cause infectious disease [source: Kates].
However, according to a 2005 study published in the British Journal of Infection Control, this bacterial source has never actually led to a case of patient illness [source: Gould].
And at least one study has shown that having flowers in a hospital room makes patients feel better. A 2008 study in the journal of the American Society for Horticultural Science revealed that patients in hospital rooms containing flowers or potted plants used less pain medication and had lower blood pressure than patients in rooms without them [source: Park].
If you weigh, then, the apparently negligible chance that floral bacteria could make a patient ill with the very real possibility that flowers make people feel better (and actually increase the oxygen supply), the decision -- to send or not to send -- seems pretty cut and dried.
Flowers are as good for sick people as they are for everyone else.
For more information on flower mythology and old wives' tales, look over the links on the next page.