Many people find themselves asking, “How can I change the color of my hydrangeas?” Hydrangeas are fascinating in that, unlike most other plants, the color of their flowers can change dramatically.
It is much easier to change a hydrangea from pink to blue than it is from blue to pink. Changing a hydrangea from pink to blue entails adding aluminum to the soil. Changing from blue to pink means subtracting aluminum from the soil or taking it out of reach of the hydrangea.
If you decided that you want to change the color of your hydrangea you will have to change the soil pH. The first step would be to know what your current soil pH is. The best way to determine this is to get a soil test. Once you get your soil test results back, you will know what the soil pH is and whether you need to increase or decrease it to get your desired flower color. To increase soil pH, you will need to add lime to the soil. To decrease soil pH, you will need to add sulfur to the soil.
Turning Pink (from Blue)
To do this you will grow the plant in a container and make the soil pH more alkaline by adding lime.
Use garden lime (calcium hydroxide, Ca(OH)2) to make the soil more alkaline. Your product should have instructions for correct application amounts.
This will stop the plant’s ability to absorb any aluminum present. Without aluminum, the color shifts to pink.
Turning Blue (from Pink)
Hydrangeas turn blue based on the pH of the soil they are in. A pH lower than 6.0 will typically give you blue or lavender-hued flowers. When the pH is above 7.0 (alkaline), it gives pinks and reds. If you have a pink hydrangea and you want it to be blue, you need to bring those pH levels down in the soil. You can do this by adding sulfur or aluminum sulfate to the soil itself.
If your blooms are currently pink, that means your soil is naturally alkaline. You can turn them blue by adjusting this and making the soil acidic. Using an aluminum sulfate to keep them blue? Add about 4 tablespoons of it to a gallon of water and drench the base of the plant about every 2 to 4 weeks.