This Reader's Digest article says:

Increase cut flowers’ longevity Freshly cut flowers will stay fresh longer if you add 1/4 teaspoon bleach per quart (1 liter) of vase water. Another popular recipe calls for 3 drops bleach and 1 teaspoon sugar in 1 quart (1 liter) water. This will also keep the water from getting cloudy and inhibit the growth of bacteria.

Is there any proof? I would imagine bleach would be toxic to flowers.

  • 2
    My wife also adds a penny; apparently the copper helps in some fashion. Note that tap water has some minor amount of chlorine in it already to kill microorganisms. – Bryce Jun 20 '12 at 10:31
  • The amount of chlorine in tap water depends heavily on your water source. I was also under the (possibly incorrect) assumption that if you left tap water to sit uncovered overnight, the chlorine would evaporate out of it. @Bryce, Copper is a antimicrobial but who knows how much is required for a significant effect. – Sam I Am Jun 20 '12 at 12:41
  • This might also be an appropriate question over at Gardening & Landscaping. – Flimzy Jun 20 '12 at 16:45

Scientific American:

[...] while water and sugar keep the flowers fresh, this mixture also encourages bacterial growth, which can harm the flowers.

"So add bleach," says Susan Han, a professor in the plant, soil and insect science department at the University of Massachusetts Amherst.

A little bleach kills the bacteria without damaging the flowers.

The Royal Society of Chemistry:

Bleach kills bacteria.

The flower stems have water channels. Bacteria clog up these channels - the bleach kills the bacteria.

University of Nebraska:

The acidity of the lemon-lime soda or vinegar lowers the pH of the water so bacteria don't grow well; the chlorine bleach kills bacteria on the stems and the sugar provides food for the flower.


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  • Note: Click the links to learn how much bleach should be used – Oliver_C Jun 20 '12 at 21:40

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