azndc/Getty Images If your hydrangea blooms are pink instead of blue—or vice versa—there's a way to get the color you want. Here's how to change hydrangea color for the perfect hue. The plant tags on your ‘Endless Summer’ hydrangeas promised beautiful sky-blue flowers—so why are the blooms completely pink? For how to change hydrangea color, take a closer look at the dirt they’re growing in. Here’s the Secret… It’s in the soil! The key to color-changing hydrangeas is whether the soil is acidic (low pH) or alkaline (high pH.) In order for hydrangeas to be a beautiful blue, the soil must be on the acidic side, with a pH lower than six. You can test this with a soil pH meter like this one. You can also look at your hydrangea blooms: If they’re pink, then the soil is alkaline.