University of Vermont Extension 
Department of Plant and Soil Science

News Article

By Dr. Leonard Perry, Extension Professor
University of Vermont

The main reason most of us grow flowers is for their colors. The color provided by flowers and the combinations of colors, and the feelings these evoke, is the main reason I and others I know garden. Yet have you ever thought about what makes flowers the colors that they are or how you can describe these colors to others?

What may seem simple on the surface is really a lot more complicated than you might think. The color that you see in flowers is actually the result of reflected light from various plant pigments.

A group of compounds called "anthocyanidins" are the basic ingredients. They are named for the flowers in which they were first found, such as the scarlet "pelargonidin" from the geranium or Pelargonium, the purple "petunidin" from the Petunia, or the blue-violet "delphinidin" from the Delphinium.

It is these anthocyanidin pigments that biotechnologists are studying to change flower colors. For instance, they've taken the scarlet pelargonidin-producing gene from corn and placed it into petunias to give this flower a novel orange color.

The gene for delphinidin (blue-violet) has been placed into carnations to make some blue. Other factors within the cell, such as the acidity (pH) and even cell shape, are making the genetic production of blue mums and roses a bit more challenging.

Combine the anthocyanidin compounds with sugar in plants to produce the more common "anthocyanin" pigments responsible for our fall leaf colors, among other colors. There are other pigments in leaves as well, such as the flavonols (yellow) and, of course, chlorophyll (green). Flavonols, and the colorless (to us) flavonoid pigments, not only affect the color caused by primary pigments (co-pigmentation), but by absorbing ultraviolet light they also are readily seen by insects.

It is the insects and other pollinators, such as moths, for whom flower colors really exist, not for our pleasure. Pollination, and subsequent fruit production, is the main purpose of most flowers. A bee balm (Monarda) that appears red to us, may appear white to an insect. Or what are white and yellow flowers to us may appear light blue to insects.

Ever wonder why some flowers such as lungworts (Pulmonaria), forget-me-nots (Myosotis), or other members of the Borage family seem to change color from pink to blue? Other flowers such as larkspur (Delphinium) also may exhibit these changes. This usually indicates to insects that a flower has aged and is past pollination, so move on!

Many flowers may not change color on an individual plant, but may change color, even if slightly, among locations or various conditions. Temperature affects color, hence, there are often more vivid colors in cool northern gardens than hot summer ones. Plant stress, such as from drought, insect attack, or plant nutrition (too much or little) also can cause different levels of pigments in flowers, and. as a result, different colors.

So the next time you look at flowers in your garden, a catalog, or in a book, think about all those unseen chemicals that cause the color. Think, too, about who in the insect world these flower colors are designed to attract, and what colors they may be seeing!

And if the color isn't as you thought described or imagined, consider why the color may be different. Believe me. You just won't think about flower colors the same way you once did!

Return to Perry's Perennial Pages, Articles