Any of the macrophylla (big leaf hydrangea) or serrate (mountain hydrangea) have the ability to change bloom color. Bloom colors range from blue to pink and all the shades in between, depending on the pH of the soil. pH is a measure of how acidic or alkaline the soil is. Low pH, below a 7 on a scale from 0 to 14, will produce blooms in the blue range. Soils with a high pH, above 7, will produce blooms in the pink range.
A soil test is the best way to determine what the soil pH is. Testing is available at English Gardens.
The availability of aluminum in the soil, and soil pH below 6, helps make the blooms blue. Depending on the existing pH, apply Espoma Soil Acidifier or Aluminum Sulfate every month to achieve the desired shade of blue.
Add garden lime to increase soil alkalinity and turn blooms pink. Color may vary from season to season due to weather, plant stress and changes in the environment. Plants near a concrete foundation or walkway may never turn blue because of the lime that leaches out of the concrete.
Altering your soil to change a hydrangea’s color is not a one-time thing. You’ll have to continually add minerals to maintain the altered soil conditions.
Visit any English Gardens location and talk with an expert for more information.
Watch our video to learn more.