If your hydrangea flowers are pink instead of blue — or vice versa — there's a way to get the color you want. Here's how to change a hydrangea color to the perfect hue. The plant tags on your 'Endless Summer' hydrangeas promised beautiful sky-blue flowers—so why are the flowers completely pink? To learn how to change the color of hydrangeas, take a close look at the dirt they grow in. Here is the secret… It's in the soil! The key to color change for hydrangeas is whether the soil is acidic (low pH) or alkaline (high pH.) For hydrangeas to have a beautiful blue color, the soil should be on the acidic side, with a pH less than six. You can test this with a soil pH meter like this one. You can also check your hydrangea flowers: if they are pink, the soil is alkaline. Which hydrangea changes color? Before you think about changing your soil, know that not all hydrangeas change color. Hydrangeas with white or ivory flowers such as Oakleaf, 'Beige' or ...