After a visit to a flower garden in California, my daughter’s favor flower is the Hydrangea. In the garden were pink, blue, light purple, and white lovely hydrangea flowers blooming all together everywhere. It was a very beautiful scene to see and enjoy.

This spring, I started to grow a Hydrangea Macrophylla plant in my garden. The Hydrangea plant that I selected for my initial trial is from the “Endless Summer” Hydrangea collection. This plant is able to bloom consistently on both old and new wood year after year. Therefore, my garden will have beautiful flowers every year during the summer. I am very excited about this plant because the color of its flower is determined by the pH makeup of the soil. The color of the flower changes depending on its growing environment and will reveal the pH of the soil. This reminds me about chemistry and basic pH measurements and titration end-point changes. The hydrangea flower is just like a pH indicator dye that we use to check the acidity and alkalinity of an unknown solution. The dye shows us the acidity or alkalinity of the solution by a color change of the indicator dye in the test solution. In this case, the color of the hydrangea flower tells us the pH (acidity or alkalinity ) of our garden soil.

Pink Flower -->Alkaline Soil (pH Above 6.0)    

 Blue Flower --> Acidic Soil (pH Below 5.5)             

Since the color of the Hydrangea flower changes with respect to the soil’s pH, we can alter the flower color by changing the soil using simple chemistry. Flower chemistry can create one’s favor flower color.

For example, the hydrangea plant that I bought is producing very beautiful light blue flowers in July indicating that my garden soil is in the acidic side. But my neighbor a few houses down the street, has a hydrangea plant with pink flowers next to the concrete walkway. This indicates that their soil is on the alkaline side. Although we are in the same area, the soil pH can be affected by its surrounding environments, such as the concrete walkway. With time, concrete will leach lime and raising the soil pH to above 6. Hence, the hydrangea flowers exhibit a pink color.

The color of the hydrangea flower can also be manipulated by applying different garden chemicals such as fertilizers, aluminum sulfate, iron sulfate, garden sulfur, or lime. The following raise or lower a soil’s pH to create a desired color:

Pink Flower : Lime

Blue Flower : Aluminum Sulfate

Soft Blue Flower: Iron Sulfate, Garden Sulfur

Instead of using chemicals, organic matter such as peat moss or composted leaves can also be used to lower the soil pH to produce blue flowers. When peat moss and leaves decompose, acidic materials such as organic acids will form. These breakdown materials are acidic and transform the soil pH to the acidic side. Hence, the flower changes to blue or soft blue. This is a “Green” method using basic natural resources available in the garden. Covering the hydrangea plant with leaves over the winter for protection will also provide beautiful blue flowers to enjoy next year.

Another way to change the soil pH is using water with a known pH, such as a weak vinegar water solution with a pH of around 5. Watering and wetting the soil periodically with this solution during the growing season will change the color of the flower. A pH range between 5.2 and 5.5 will generate flowers with a beautiful light-purplish-blue color. It is my favor color.

The Hydrangea is a fascinating flowering plant. The color of its flower can tell us about the environment and the pH of the soil. We can create different color flowers from the plant by applying simple chemistry to gardening.