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Changing Colours of Hydrangeas

Rules of genetics decide the colour of a flower, we have learnt that. It is true however there is a plant that produces different colours of flowers in different types of soils. Yes! That plant is Hydrangea macrophylla. Let's read how that happens!!

Hydrangea macrophylla is known as hydrangeas and are ornamental plants found commonly in gardens. The plant produces pink flowers in basic soils and blue in acidic soils. How does that happen though?

What is pH?

pH scale

pH depends on the concentration of hydrogen ions in the medium. More hydrogen ions indicate a low pH and acidic nature. Fewer hydrogen ions indicate a basic pH. pH of the soil can be affected due to many reasons like rainfall, the basic core of soil etc.

How does the pH of soil change the colour of flowers?


The colour of the flowers of the hydrangeas is due to an anthocyanin pigment. These chemical compounds have alternating double bonds which can absorb light and reflect the contrary colour. delphinidin-3-glucoside belongs to the family of anthocyanin. At lower pH, this molecule can give up its hydrogens to make a negative entity to balance out the effect of hydrogen cations.

Another factor which is responsible for this colour alteration is aluminium ions. In acidic soils, this aluminium is easily available and can be uptaken by plants via roots. In basic soils, however, these ions form bonds with basic groups like hydroxide and thus cannot be taken up by the plant.

This aluminium ion is found to play a role in the mechanism of colour switching. The anionic species that is formed due to low pH conditions, chelates with the aluminium ion present in the plant. This chelated compound now works differently than the original colour-giving compound. The chelation with aluminium ion shifts the colour from red to blue.

How to change the colours of your hydrangeas?


Hydrangeas are a common plant found in gardens and small backyard nurseries. To change the colour of the flowers alter the pH of the soil. To make the soil basic, quick lime can be added to it. Compounds like sulphur are used to decrease the pH of the soil.

The addition of aluminium is also advised to shift the colour in the blue spectrum.

There are always exceptions hence, not all types of hydrangeas change colour with the pH of the soil. If your hobby is farming, make out a fun activity and project by changing the colours of the hydrangeas in your backyard.



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