Mix 1 pint lemon-lime soda, 1 pint water, 1 teaspoon mouthwash, and 1–2 drops of dish soap; Missouri Extension says the mix can help cut flowers last up to twice as long

In between doom-scrolling and acting like you have a skin care routine, a weird hack has been making the rounds: a flat lemon-lime soda, a splash of mouthwash, and a couple of drops of dish soap in a vase. This homemade mixture doubles the longevity of cut flowers left in plain water, according to horticulturist David Trinklein in a University of Missouri Extension article That's not a minor assertion for a generation that considers the $70 bouquet from the grocery store a worthy mood booster.

The biology nobody explains when they hand you a bouquet

A cut flower doesn't die of old age. It dies because water loss outpaces its capacity to take up fresh water, mostly because bacteria growing in the vase clog the xylem, the tissue responsible for moving water up the stem. Sunlight, warmth, and drafty window sills simply speed the process along. The problem isn't that the flower is too delicate for the water, it's that bacteria in that water are choking off its supply, leaving the bloom effectively parched even while it's sitting in liquid.

The commercial flower food solves the problem with the help of three simple ingredients: sugar for energy, acid to slow down bacterial growth, and an antibacterial agent. The soda and mouthwash mixture serves the same purpose: citric acid and sugar from the soda, a bacteria-killing agent from the mouthwash, and dish soap as the wetting agent to facilitate water flowing through the stem.

Researchers have actually tested it

This one has receipts. Citrus sodas such as 7-Up actually do make vase water sugary enough and acidic enough to help prolong the life of the flowers, Susan Han, a plant physiologist at the University of Massachusetts Amherst, told Live Science in a 2013 article. But not all kitchen-cabinet lore holds up: the same 2013 report noted that dropping a copper penny into the vase does nothing, because the copper in modern pennies isn't soluble.

This mechanism is also seen in the real world of science in the lab, and not only in florist stories. In a 2020 peer-reviewed study titled “Nanosilver as a novel biocide for control of senescence in garden cosmos,” published in Scientific Reports, the researchers found that the mixture of biocide and sucrose proved to be the most effective in prolonging cut-flower vase life by 53-69 per cent, compared to just sugar or biocide alone, which had little effect. That's essentially the scientific foundation behind any DIY flower recipe, homemade or store-bought.

How to actually make it

This is Trinklein's exact recipe, according to the Missouri Extension: one pint of a non-diet lemon-lime soda, 1 pint of water, 1 teaspoon of antiseptic mouthwash (Listerine or Scope, and not the blue one you use to feel better after drinking too much), and 1-2 drops of dish soap. Cut approximately an inch off the stems at an angle when placing them in, as this will not allow an air bubble to block water uptake.

A necessary reality check

None of it makes flowers last forever. Even Trinklein is forthright that preservatives are not meant to last a lifetime, and that a rose's appeal may well be its brief existence. No, this hack isn't going to make a $12 bouquet of groceries a permanent feature. What it will accomplish is to give those days of good flowers a week or more, with materials you already have in your medicine cabinet and refrigerator. It isn't a lifestyle trend or a substitute for expensive self-care products, it's straightforward chemistry, borrowed from a decades-old university extension recipe and put to a more everyday use than a science fair project.