From the manufacturer Westland Hydrangea Colourant 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. Key Benefits Changes pink hydrangeas to blue Easily absorbs nutrients Nitrogen for greener leaves Potassium to boost flowering What to expect Pink Hydrangeas will produce blue flowers and darker pink Hydrangeas will be mauve. How to use Established shrubs Mix the Hydrangea Colourant into the soil at the rate of 50g per square metre. Every 7 days during the growing season dissolve 50g of hydrangea colourant in 5 litres of water and apply to the area of soil covered by the shrub. Do not apply directly on plant foliage. Container-grown Hydrangeas When potting, mix the Hydrangea Colourant into the compost at the rate of 50g per 5 litres of compost. Every 7 days during the growing season dissolve 50g of hydrangea colourant in 5 litres of water and water the soil round the plant. Best results are obtained with plants growing in acid soils. Where the soil is naturally alkaline use an Ericaceous compost (such as John Innes Ericaceous Compost or Gro-Sure Ericaceous Compost) instead or double the application rate When to use Apply Westland Hydrangea Colourant between April and September Some Hydrangeas are bred to show pink flowers in all conditions — please check the plant label.Do not apply Hydrangea Colourant directly on plant foliage.Best results are obtained with plants growing in acid soils.Where the soil is naturally alkaline use an Ericaceous compost (such as John Innes Ericaceous Compost or Gro-Sure Ericaceous Compost) instead or double the application rateHydrangea Colourant doesn’t contain any organic elements so shouldn’t be attractive to animals.