In 1963 a man named Ralph Farrar was diagnosed with a disease called
Hemochromatosis. The result was that his blood had too much iron. The treatment at the time—which is still recommended today—is removal of blood from the body on a regular basis. Once a week, Farrar would go to the doctor where they would remove a pint of his blood.
Blood taken for this purpose cannot be used as part of a blood bank, so he found another use. Once a week he would pour a bottle on his roses as an iron-rich fertilizer. Ralph lived in San Antonio, Texas, but his story was picked up by the Associated Press (AP). Here is an archive of the original article as it appeared in the Tuscaloosa News on June 29, 1963.
Of course, the most famous plant that demanded blood was Audrey II, the plant from Little Shop of Horrors, which started as a 1960 Roger Corman film, then became a popular Broadway musical, finally returning to film in 1986, directed by Frank Oz.