Why Use a Flower Preservative?

The simple answer to this question is that flower preservatives are designed to make your flowers last as long as possible. Most preservatives have three main ingredients that help achieve this:

A Germicide

Cut flowers need to take up clean water to stop them wilting. Germicides keep the vase water clean by killing bacteria, fungi and other micro-organisms that always proliferate in vases of cut flowers. These micro-organisms are on all flower stems, the vase surface and even in tap water. They feed on sugar, which is contained in the sap that leaks out of the cut flower stem ends. Happy bugs also multiply and can very quickly block the cut stem ends. Stick a bandaid over our mouth and try to suck up water and you'll know how the flower feels in dirty water! Common germicides used in preservatives are chlorine or bromine.

Sugar

Flowers need sugar to open and keep those colourful petals bright. Sugar is also needed to keep fragrant flowers smelling so good. When they are on the plant this sugar comes from the leaves, where it is made during photosynthesis. Once you cut a flower off the plant and place it inside where it is too dark for photosynthesis to occur, that sugar is gone, and the flower dies. The sugar in a preservative is taken up through the cut stem end and feeds the flowers and buds, keeping them alive. Because micro-organisms thrive on sugar, however, don't ever add sugar without a germicide as this will cause a bacterial soup in the vase water before you can blink.

Acidifier

Cut flowers take up far more water if the water is slightly acid in nature. A pH of 3.5 is ideal. So, many preservatives contain a gentle acid, like citric acid, that will slightly acidify the water. Vinegar (acetic acid) will also work fine. Incidentally it's not entirely certain why cut flowers take up more water when it's slightly acidic.

Make your own Preservative

It's easier to use a sachet of commercial preservative, but if you don't have one:

To 1 litre of water add:

1 teaspoon of bleach

2 teaspoons (10 g) of sugar

1 teaspoon (5 ml) of vinegar

3 pinches (0.3g) of citric acid.