Vitax Hydrangea Colourant 500g adjusts flower colour by supplying iron and aluminium salts, encouraging blue hues in hydrangeas. It is especially effective on pale pink varieties, which shift to blue, while darker pinks transition to mauve or blue shades. For optimal results, apply on hydrangeas grown in acidic soil. This 500g pack provides sufficient treatment to enhance the natural colour of your hydrangeas with precision.