Hydrangeas are a southern staple! Large mop head blooms of blue or pink flowers hiding out in the afternoon shade during the hot Louisiana summers makes me feel at home! Over the years people have learned that they can change the colors of their hydrangea. Awesome! Today we learn the science behind the color of the Hydrangea Bloom.
Aluminum – that is it!
This metal is responsible for turning the sepals of the bloom blue. The AVAILABLILITY and PRESENCE of it is the key. In low pH conditions, Aluminum is released into the soil and absorbed up into the plant. The presence of this metal in the flower will give it a blue hue. In high pH conditions, Aluminum is bound by ions and held onto in the soil. Not able to take in the metal, the plant will produce flowers lacking Aluminum, causing them to be pink.
So to make yours blue, add Aluminum Sulfate. It adds the Aluminum to the soil while decreasing the pH, making it available to the plant. Adding lime to the soil will raise the pH, binding the Aluminum in the soil. Thus not allowing the plant to absorb the metal.
Some general rules…
White hydrangeas are white… They cannot be changed. Genetically they lack pigments that will respond to the Aluminum in the soil. Some “Red” Hydrangeas that have been breed to be red, cannot be turned blue. They will turn a lighter or faded pink, but not blue.
Most Hydrangeas will be blue due to the natural soil in our area. To change their color is not an immediate thing, it can take up to a year to change the pH and in turn the color of the blooms…
In the meantime, hideout in the shade with your classic blue, pink or white Hydrangeas.