Many people are familiar with the concept of dyeing flowers with food coloring. But did you ever stop to think about the underlying process that occurs when you dye flowers using just colored water? The structure of the plant and natural processes like transpiration and cohesion enable many flowers to readily absorb the food coloring and deposit the dye on their petals.

...
Carnations easily absorb dye

Dyeing Process

When a cut flower is placed in dye, the dye is pulled up the stem and absorbed along with the water. As transpiration causes the water to evaporate from the leaves, the dye is left behind on the petals. The entire dyeing process can take anywhere from a few hours to a few days, depending on the conditions, the flowers and the dyes.

Transpiration

The process of transpiration refers to the evaporation of water from a plant's leaves. The majority of water inside of a plant is eventually lost through transpiration. The loss of water through the leaves creates low pressure in the leaves, which leads the plant to pull more water up through the stem, much like a straw. Once the water begins to travel up the plant's vessel system, cohesion causes the water molecules to stick together and continue to move up the stem.

Flowers

White daisies and carnations are generally the two flowers most recommended for dyeing, although any long-stemmed flower will work. Daisy petals can be dyed completely; carnations typically display the color of the dye while still maintaining a little whiteness on the petals. Whichever flower you choose, the dyeing process will be most successful if you select a fresh flower, rather than one that is in full bloom or wilted.

Factors

The dye works best with very warm to hot water since heat acts as a catalyst. Similarly, warmer air temperature will also speed up the water absorption and dyeing process. Different color dyes seem to work at different rates due to the chemical makeup of the dye, while different brands of food coloring also affect the rate of color absorption. Experiments indicate that blue dye is most effective, followed by red dye and then green dye.

Tips

Recut the stem diagonally under water before placing the flower in dyed water. This encourages the flow of water up the flower stem and prevents any air bubbles from forming at the base of the stem. Florists suggest adding a floral preservative to the water to extend the life of your flowers as you dye them. Experts also recommend using 30 to 40 drops of food coloring in order to achieve the desired color.