For hydrangea blooms to be pink, the plants must not take up aluminum from the soil. If the soil naturally contains aluminum, one must try to keep it away from the hydrangea’s system. Try adding dolomitic lime several times a year or use a fertilizer with high levels of phosphorus (phosphorus helps to prevent aluminum from creeping into the system of the hydrangea) or in areas that naturally produce blue hydrangeas (soils with aluminum), consider growing pink hydrangeas in large pots where t will be much easier to control the requirements for growing pink hydrangeas.
To obtain a blue hydrangea, aluminum must be present in the soil. To ensure that aluminum is present, aluminum sulfate may be added to the soil around the hydrangeas.
White hydrangeas can not be changed to pink or blue by the grower.
If you live in a hot climate, it is unlikely you will ever see a “true red”” hydrangea. No matter how much lime is added to the soil
