Hydrangeas are beautiful flowering plants that can bring a pop of color to any garden or landscape. One of the fascinating aspects of hydrangeas is their ability to change color, particularly when it comes to turning purple. In order to understand why hydrangeas turn purple, we need to delve into the science behind it.
The color of hydrangea blooms is influenced by the soil pH. pH is a measure of the acidity or alkalinity of the soil, ranging from 0 to 14. A pH of 7 is considered neutral, below 7 is acidic, and above 7 is alkaline. Hydrangeas typically thrive in slightly acidic to neutral soil, with a pH range of 6 to 7.
When the soil pH is in the lower end of this range, around 6, hydrangea blooms tend to turn purple or bluish-pink. This color change is due to a pigment called anthocyanin. Anthocyanin is responsible for the blue and purple hues in flowers, fruits, and vegetables.
So, how does soil pH affect the color of hydrangea blooms? Well, when the soil is acidic, aluminum ions are more readily available to the plant. These aluminum ions are taken up by the hydrangea roots and transported to the petals of the blooms. In an acidic environment, the aluminum ions combine with the anthocyanin pigment, resulting in a bluish-purple color.
On the other hand, when the soil pH is more alkaline, above 7, the availability of aluminum ions decreases. Instead, other pigments, such as flavonols, become more prominent, giving the blooms a pink or even red color. This is why you might notice hydrangeas turning pink in more alkaline soil.
Now that we understand the role of soil pH in hydrangea color change, let’s talk about how to manipulate the pH to achieve the desired purple or bluish-pink blooms.
To lower the pH and encourage purple or bluish-pink blooms, you can add garden sulfur or aluminum sulfate to your soil. These products are available at garden centers and come with instructions on how much to use based on your soil type and desired pH adjustment. It’s important to follow the directions carefully to avoid over-acidifying the soil, which can harm the plant.
If, on the other hand, you want to raise the pH and promote pink blooms, you can use ground lime. Again, make sure to follow the instructions provided with the product to achieve the desired pH level without overdoing it.
It’s crucial to mention that altering soil pH is not an immediate process. It takes time for the amendments to break down and affect the soil chemistry. Therefore, it’s recommended to test your soil pH periodically to monitor the progress and make adjustments as needed.
Hydrangeas turn purple or bluish-pink due to the presence of aluminum ions and the acidity of the soil. By manipulating the soil pH, you can influence the color of the blooms. Garden sulfur or aluminum sulfate can lower the pH for purple blooms, while ground lime can raise the pH for pink blooms. Remember to follow the instructions provided with the products and test your soil regularly to ensure your hydrangeas are thriving in the desired pH range. Happy gardening!
