Westland Hydrangea Colourant is a salt which changes pink hydrangea varieties to blue. It also changes darker pink varieties to mauve blue. This colourant easily absorbs nutrients, as well as nitrogen for greener leaves.   When using Westland Hydrangea Colourant, obtain the best results with plants growing in acid soils. Use ericaceous compost where the soil is naturally alkaline and alternatively, double the application rate. A combination of iron and aluminium salts Acidifies the soil to produce blue flowers Potassium to boost flowering Why Use To help rooting and establishment of cuttings What to Expect   Pink Hydrangeas will produce blue flowers and darker pink Hydrangeas will be mauve. Some Hydrangeas are bred to show pink flowers in all conditions — please check the plant label.