“Add a penny with a pinch of sugar into the vase of cut flowers to have them last twice as long!”
There are a lot of myths out there on what you can do to prolong the beauty of cut flowers. Everything from vodka, bleach, even aspirin is said to help. This one here is an old wives’ tale that has been around for so long that I doubt anyone knows where it came from. I remember my grandmother doing this when she bought fresh flowers. But can a copper penny prolong the life of your flowers? No, not really.
Let’s start with the water. Tap water is regulated quite strictly; all tap water must maintain a pH level between 6.5-8.5, which is round about the center of pH levels. I’ve spent quite some time trying to research if copper can alter the pH level of water at all, with no luck of finding any data on this I turned to a chemistry-knowledgeable friend of mine who informed me “Copper does not react with pure water, so it should not affect the pH. If you’re talking about tap water, that’s a lot more complicated and dependent on the particular contaminants. I’m sure there are side reactions with the other particles that could slightly affect pH, but nothing major since the contaminants are in low quantities.”
Why does this matter? Because most cut flowers prefer a higher acidic water. According to a great page by the Horticulture Department of Minnesota – “An acidifier makes the pH of the water more near the acid pH of the cell sap. Most water supplies are alkaline and can reduce the life of cut flowers. The acidifier also stabilizes the pigment and the color of the flower.” (source)
Commercial flower preservatives are made up of basically 3 things: sugar, an acidifier to prevent the growth of microorganisms, and a respiratory inhibitor. If copper does not affect the pH levels, perhaps it acts as an antimicrobial in another way, but the results of copper as an antimicrobial are largely debated (source). In large quantities it looks like it might help limit the growth of microbes, but the small amount of copper found on a penny isn’t going to do that. It’s important to point out that most pennies in circulation today were made after 1982, and are not pure copper. Instead, they are copper-plated zinc and only contain a thin coating of copper on the outside. However, adding a pinch of sugar to the water isn’t a bad idea, but it won’t get you the same results as a commercial cut flower food will. You’re best bet if you don’t have any plant food on hand is to just make sure you change the water daily, keep any leaves or foliage out of the water, and a pinch of sugar can’t hurt (but leave the pennies in the change jar).
If you’re looking on more information on myths of cut flowers, here is a great article by Terril A Nell, PhD, who was chairman of the flower research program at the University of Florida. He touches base on pretty much every flower myth and explains why they aren’t true.