Hydrangeas – Nature’s Litmus Test

Pink Hydrangeas in alkaline soil

Hydrangeas are nature’s litmus test, by which I mean they can tell us the pH of the soil they are growing in.

There are actually dozens of Hydrangea species within the genus, but we are interested in a very common one, especially in gardens: Hydrangea macrophylla. Horticulturalists know it better as ‘Hortensia’.

The flowers of this plant are sensitive to soil pH and change colour to reflect changes in acidity.

Pink Hydrangeas indicate soil that is alkaline to neutral. Blue flowers indicate soil that is acidic.

Technically the plants are reacting to differing levels of aluminium ions, but the effect is all we need focus on in terms of reading a landscape.

The photos on this page were all taken in the Subtropical Gardens at Abbotsbury in Dorset. It was a treat to be able to watch the colours change from blue, through purple to pink as the soil changed dramatically over short distances.

Blue Hydrangeas in acid soil
Purple Hydrangeas in neutral soil

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