Dr Abe V Rotor
Hydrangea macrophylla. The color of the flower indicates the relative acidity of the soil. An acidic soil (pH below 6) produces flower color closer to blue (top photo), whereas an alkaline soil (pH above 6) will produce flowers more pink (middle photo). This is caused by a color change of the flower pigment in the presence of aluminum ions accumulated in the plants. Lowermost photo indicates slightly alkaline soil, and possibly of another cultivar.