Question

Hydrangea is a flower that presents in a variety colors including blue, white and pink. The color of some varieties of

hydrangea flowers can be controlled by the gardener growing the plant in a container and carefully regulating the pH. In
some instances aluminum sulfate, Al2(SO4)3, must be added as well. Perform an on-line search to identify what pH range
favors pink and blue color petals on hydrangea flowers. Also comment on the role of aluminum sulfate in determining the
color of the flower.

Answer 1

Bigleaf hydrangeas are blue if the pH is between 5.0 and 5.5. The flowers

turn pink when the pH gets around 6.0. The flower color is dependent on

the concentration of aluminum ions (Al+++) in the soil. Aluminum is more

available to the plant when the soil is acidic, less available when the soil is

alkaline.The color of the cultivar called “Endless Summer” of H. macrophylla depends

on soil pH. Red or pink blooms result from neutral or basic soil (pH 7 and

above), whereas blue blooms indicate acidic conditions (pH less than 7).