Stuart Williamson of Dunedin asks :-

Why do cut flowers in a vase look fresher, have brighter colours, and last longer if flat lemonade is added to the vase water?

Mike Morley-Bunker, a horticulturalist at Lincoln University, responded.

Flowers are fresh living tissues and, therefore, need the conditions and inputs that allow metabolism to continue. Of course you may want to slow the rate of metabolism to prolong the life of the harvested flower but you don't want to stop flowers doing what they need to do - metabolise.

The principal input for the respiration process - part of the overall metabolism activity - is carbohydrate. Sugar is a very accessible and easily used carbohydrate for the process of respiration. Flowers that have been separated from the plant have lost the main source of soluble sugar. The store of soluble sugars in their own tissues can be exhausted within days if not hours. The addition of sugar to vase water will assist the flowers respiring tissues.

Sugar in water can also provide the respiration inputs for any bacteria and micro-organisms present in some water. Vase water, with added sugar can quite quickly become cloudy as the growth of micro-organisms becomes obvious. Flower stems and the flower tissues that transport water up the stems can become coated and clogged with micro-organisms. So unfortunately sugar alone, as a vase water additive, can cause more problems than water alone. So the next problem to solve is preventing micro-organism growth.

The best means for this is to use compounds that can be termed antibacterial or biocides. These compounds need to be relatively specific for this role with cut flowers because some biocide compounds have properties that can harm flower tissues as well as the micro-organisms. Commercial vase solutions, designed to prolong the life of cut flowers, will have an appropriately chosen biocide.

Some limited control of micro-organism growth can be obtained if the vase solution is relatively acid. A slightly acid solution also promotes better water uptake by the flower tissues. Acids that can be used (at the appropriate concentration) include citric acid, which is found in most lemon drink products.

Carbonated (fizzy) lemonade drinks will have sugars, citric acid and dissolved carbon dioxide (which is the source of the "fizz"). Carbonated water will not assist respiration but once the dissolved carbon dioxide has been expelled, and the drink is said to be flat, you have a drink which has sugar and acid present. This solution can be added to vase water and it may prolong the metabolism and life of the cut flowers.

Lemonade is not an ideal addition but it can make a difference. Enquiring minds might like to take this information further and design experiments with a range of products added to vase water to see the effects on prolonging the life of cut flowers.