We all know that hydrangeas can change its color. Do you know why hydrangeas can do this? Hydrangea color change ismainly related to the acid-alkaline soil. When the soil is alkaline, PH value is greater than 7, hydrangea will open red flowers when the soil is acidic and the PH value is less than 7, blue flowers will bloom. And the depth of the flower color is also related to the PH of the soil, the higher or lower PH, the color will be darker.