Yes, for the most part you can change the color of hydrangeas, with the exception of white hydrangeas.
You can’t change their color. The only variation with white hydrangeas comes with the plants age. It will sometimes take on a hue but it really does it on its own and can’t be forced.
Want to learn how?
Change the Color of Hydrangeas:
To change the color of hydrangeas it is a matter of adding or subtracting minerals to the soil. Changing the color of hydrangeas that are potted is a much simpler task.
You have complete control over the soil the plant is contained in. Turning bushes that are planted in the ground is a little tricker because you are changing the PH levels of the soil. Acidic soil contains a higher aluminum content and will turn flowers blue. If the soil has an alkaline base, the flowers turn pink.
Pink to Blue Hydrangeas:
Water your bush well. Mix up 1 Tablespoon of aluminum sulfate per gallon of water. Feed your bush throughout the growing season. You can also feed your plant coffee grounds and grass clipping to help maintain the coloring between aluminum sulfate additions.
Blue to Pink Hydrangeas:
If your bush is naturally blue in color, you will need to block the plant from leaching aluminum from the soil. The only way I have heard to do this is to add dolomitic lime many times a year. This will change the PH level of the soil. Water your soil really good in the morning and work 1-2 cups of dolomitic into toward evening. Do this a few times during the growing season.
Look for a fertilizer with high phosphorus level to fertilize the bush. Look for one with a 25/10/10 . Underlined is the phosphorus number
As you can see. It is pretty simple to change the colors of your hydrangeas.