Hydrangeas are sometimes called “the mood ring of plants” due to their ability to change color depending on where they are planted. These colorful shrubs bloom from early spring until late autumn, and bloom in white (limelight hydrangeas) or varying hues of red, blue, or purple (macrophylla hydrangeas). Those who purchase hydrangeas seeking a specific color are often confused or frustrated when the bright blue hydrangeas they planted last year are producing pink flowers (or vice versa) this year!
So what determines the color of your hydrangeas? And how can you ensure that your plants will stay the color you want them? Other than limelight hydrangeas, which are white and do not change color, the hue of your hydrangeas depends on the soil composition where you plant them, specifically the pH level of the soil.
For macrophylla hydrangeas to bloom in a red or pink hue, the soil must be more alkaline (or less acidic) so a pH between 6.0 and 6.2 is ideal. For the highly sought-after blue flowers, the desired pH is between 5.2 and and 5.5.
Many gardeners wish to measure their soil’s pH level before planting their hydrangeas to ensure they can maintain their desired bloom color. pH level is essentially the concentration of hydrogen ions in the soil, and be easily measured with a store-bought pH testing kit or on your own with some distilled white vinegar. After placing a small sample of soil into a container, pour the vinegar on the soil and observe if it fizzes or bubbles. If it fizzes, it means your soil is more alkaline, and therefore will result in pinker flower. No fizz means your hydrangeas will likely bloom blue.
Luckily, modifying the color of your hydrangeas is fairly easy. As pinker flowers require more alkaline/less acidic soil composition, you can simply add Garden Lime to the area surrounding the plants. This common chemical can be found in most hardware or gardener supply stores, and should produce pinker hydrangeas by the next blooming season.
Blue flowers are achieved in a similar manner by adding aluminum sulfate to your soil. Coffee grounds, fruit and vegetables peels, or grass clippings can also be used to more naturally increase the acidity of soil.
If the hydrangeas are resistant to color change, consider planting the shrubs in large pots rather than adding them permanently to your landscape. Sometimes it can be difficult to modify soil’s existing composition, and it is especially difficult to change naturally-blue plants pink.
To maintain your adjusted-colored hydrangeas from year to year, remember to test the pH level of the surrounding soil often and adjust the amount of Garden Lime or aluminum sulfate as necessary. Without regular maintenance, soil will always revert to its original pH, and the color of your hydrangeas will follow.
For assistance with your hydrangeas or any other landscaping needs, please contact us at (910) 256-6345
