J Arthur Bower's Hydrangea Colourant is a salt which changes the colour of pale pink hydrangea varieties to blue and darker pink varieties to mauve blue.
Best results are obtained with plants growing in acid soils. Where the soil is naturally alkaline, use ericaceous compost instead or double the application rate of colourant added.
It should be noted that some Hydrangeas are bred to be pink in all soil conditions and will not change colour.
For established shrubs:
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