Certain varieties of Hydrangea can be turned blue or purple through the application of ALUM (Aluminium Sulphate) which alters the soils PH. The ideal PH to achieve the best blue is 4.3, however care should be taken to ensure the PH does not drop below 4.0 as this is likely to kill the plant.
Hydrangea macrophylla Early Blue shown in Pink and Blue.
Hydrangea macrophylla Red Beauty shown in Red and in Purple.
There are specialist fertilisers that are high in ALUM which have been formulated to turn and maintain blue colouring in Hydrangeas. These fertilisers can be purchased from Bunnings, Flower Power or your local garden centre.
Each product’s instructions may vary, as such we recommend following the instructions on the packaging to ensure the best result!