Put a penny in the vase: Wives' tale or real solution?

If you don't like to use chemicals to prolong the life of your cut flowers, there are "natural" alternatives. Some methods work better than others. Here's one for you: does a penny and an aspirin tablet placed in the vase water really do any good? Some say the combination does keep flowers fresh longer. The theory is that the copper acts a fungicide and the aspirin makes the water more acidic. Here are more food + acid combinations:

• Add one part lemon-lime soda (not diet) to 3 parts water. Then to each quart of this solution, add 1/4 teaspoon bleach. Thereafter, add 1/4 teaspoon bleach after each 4 days of use.
  
• To 1 quart water add 2 tablespoons fresh lemon juice, 1 tablespoon sugar, and 1/2 teaspoon bleach.
• Add 2 ounces Listerine mouthwash per gallon of water. Listerine contains sucrose (food) and a bactericide. Listerine is acidic and is said to help water move up the cut stem. 

From plantea.com/cutflowers