CHANGE TO PINK CHANGE TO PINK 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... to 6.2 (If it goes above 6.4 hydrangeas may experience an iron deficiency). Since hydrangeas take up aluminum best at lower pH levels, raising the pH will help to keep the bluing.... Choose a fertilizer close to the ratio of 25/10/10 (Phosphorus is the middle number). In areas that naturally produce blue hydrangeas (soils with aluminum), consider growing pink...