What makes flowers appear blue?

Back to basics for a moment!  A reminder as to how we SEE colour. All objects absorb or reflect different wavelengths of light. Those wavelengths may be in the VISIBLE RANGE of the spectrum that our eyes are sensitive to creating colours in the ranges of Reds through to Violets .. the colours of the rainbows. Whether an object .. or flower in this instance … absorbs or reflects a particular colour depends entirely on the chemicals called PIGMENTS that are present. YES IT’S ALL ABOUT PIGMENTS 


Our eyes are pretty amazing pieces of equipment. In the  retina at the back of our eyes are cone cells which contain a pigment called IODOPSIN. This pigment absorbs wavelengths of Red Blue and Green light. This information is then passed to the visual cortex of the brain where it is translated. 

At that point our brain PERCEIVES not just the COLOUR of the object we are looking at but the SHAPE of that object. It does that by identifying the borders where colour changes occur.  With information produced from both eyes, we are able to create a 3D image also allows us to create a sense distance which creates the depth of the shape.  Our PERCEPTION centres in our brain create an ever changing image of our reality in 3D.  MAGIC !!  

Optical trickery!

The colour BLUE doesn’t come that easily in plants because a true BLUE pigment doesn’t exist. Instead, other pigments called anthrocyanins, under the influence of plant minerals, combine with wavelengths of light to create the colours people see. Among all the purples, violets and reds, some naturally blue flowers emerge.

There is intense commercial interest in discovering the chemical basis for blue flowers in nature. So few of our common garden flowers produce a blue form. Biochemists have tried to genetically modify plants with a gene such as that which creates Delphinidin, the blue colouring in Delphiniums and violas in trying to make a BLUE rose, but it has to this day escaped them. Florists will dunk freshly cut flowers into blue dyed water to create the illusion of blue flowers.

My new colourful specimen from Stonyford Gardens, Cheshire

Most anthocyanins never create blue colouration if the soil they are growing in is a weakly acidic to neutral solution. The mechanism of blue-colour formation is very complicated in most cases. For example beautiful DELPHINIUMS which we associate with a number of vibrant blues to soft blues produce a pigment called DELPHINIDIN. Yet even the presence of that in bucketloads requires a particular pH and the formation of complexes of anthocyanins with flavones and metal ions to create those colours. 

The behaviour of Hydrangeas also demonstrates this. You may well have paid a lot of money for the most beautiful pink variety of this plant species, and you rush out and plant it in your naturally alkaline soil. No one has advised you differently. And suddenly you have a lavender of blue version instead. The soil ph plays such an important part in creating the rich assortment of BLUE HUES in some eye-catching varieties.  

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