What Decides The Colour Of Flowers?

Imagine a garden with no colour at all. No red roses, no yellow sunflowers, no deep blue hydrangeas. Flowers would still be there, but they would mean far less to us, and to the bees and birds that depend on them.

At The Flora, we spend every day surrounded by colour, so we wanted to answer a simple question properly. Why is a rose red and a sunflower yellow? The answer sits partly in a flower's chemistry and partly in its need to be noticed.

What Decides The Colour Of Flowers?

A flower's colour comes from pigments, natural chemicals in the cells of its petals that absorb some kinds of light and reflect the rest. The colour we see is the light they reflect. Which pigments a flower makes, and how much of each, is set by its genes.

Growing conditions can shift the final shade. The acidity of the sap in the petal, minerals in the soil, temperature and sunlight can all make the same plant bloom a little brighter, paler or bluer from one season to the next.

The Pigments Behind Flower Colours

Almost every flower colour you have seen comes from a handful of pigment families, often working together in the same petal.

1. Anthocyanins (Red, Pink, Purple And Blue)

Anthocyanins belong to a large group of plant chemicals called flavonoids. They give roses and carnations their reds and pinks, and violets and petunias their purples. The same pigment can look redder in more acidic sap and bluer in less acidic sap, which is one reason shades vary so much.

Hydrangeas show this clearly. In acidic soil the plant can take up aluminium, which binds to its anthocyanins and turns the blooms blue. In alkaline soil the same plant tends to flower pink.

2. Carotenoids (Yellow And Orange)

Carotenoids are the pigments behind the sunny yellow of sunflowers, the gold of marigolds and the orange of many chrysanthemums. They are the same family of pigments that colours carrots and mangoes. When carotenoids and anthocyanins mix in one petal, you get warm shades of coral, peach and deep orange-red.

Know More About: All About Sunflowers

3. Betalains (Magenta And Yellow)

Betalains are a rarer group of red-violet and yellow pigments found in only a few plant families. They colour the bright bracts of bougainvillea, portulaca blooms and beetroot. Plants that make betalains never make anthocyanins, so the two are never found in the same flower.

4. Chlorophyll (Green)

Chlorophyll is the green pigment that lets plants turn sunlight into food. It fills the leaves and stems, and in a few flowers, such as green chrysanthemums and some orchids, it stays in the petals too.

White flowers, such as the oriental lily, have little or no coloured pigment. Tiny air pockets inside the petal scatter all the light that reaches it, so the petal looks white.

Why Are Flowers So Brightly Coloured?

Colour is how a flower advertises. Most flowering plants need animals to carry pollen from one bloom to another, and bright petals help bees, butterflies and birds find them.

Different pollinators are drawn to different colours. Bees see blue, violet and yellow well, and they can also see ultraviolet light. Many flowers carry ultraviolet patterns, invisible to us, that guide bees straight to the nectar. Bees see red poorly, so red, tubular flowers are more often visited by birds such as sunbirds.

Plants that are pollinated by the wind, such as grasses, have no need to attract animals. Their flowers are usually small, green and easy to miss.

Know More About: How To Use Colour Theory To Make Beautiful Floral Arrangements

Why Do Flowers Have A Scent?

Scent works alongside colour. Flowers release fragrant compounds, often called essential oils, mostly from their petals, and each scent tends to suit a particular pollinator.

Not every flower smells sweet. The titan arum of Sumatra, one of the largest flowers in the world, smells like rotting meat. It needs carrion beetles and flesh flies to pollinate it, and that smell is exactly what draws them in.

Sweet scents attract bees and butterflies, while strongly fragrant white flowers that open at night, such as tuberose and jasmine, are made for moths that find them in the dark. Flowers pollinated by bats often have a musky, fruity smell.

Over millions of years, flowers and their pollinators have shaped each other, a process called coevolution. Some orchids take this a step further. Their flowers look and smell like a female bee or wasp, so males try to mate with them and leave carrying pollen to the next orchid.

Know More About: Fragrant Flowers: India's 10 Most Scented Blooms

Can Flower Colours Be Changed?

Growers have changed flower colours for centuries by crossing plants, and modern science can now move genes between species. The best known example is the so-called blue rose. Roses cannot make delphinidin, the pigment behind most truly blue flowers, so no natural rose is blue.

Researchers at Suntory in Japan and Florigene in Australia added a gene from pansies that lets a rose make delphinidin. The result was a striking rose, but it is lavender to pale mauve rather than true blue. Most blue roses you see in shops are white roses dyed blue.

Conclusion

Every colour in a bouquet has a reason behind it, from the anthocyanins in a red rose to the carotenoids in a sunflower and the light-scattering petals of a white lily. Some people would love to see unusual new shades, but we are happy with the colours flowers already bring.

If you would like to enjoy those colours at home, explore our fresh bouquets. We deliver flowers and bouquets the same day across Bangalore, Delhi, Hyderabad and Mumbai, and you can also explore our Flower Subscriptions for regular fresh blooms.

Know More About: History Of The Language Of Flowers

Author: Bhawika Jethwani