Did you know that the color that your hydrangeas bloom is dependent on the pH-level of the soil that they’re planted in? The higher the acidity (pH less than 6), the bluer your flowers! The more alkaline soil (pH greater than seven) typically results in pink-ish flowers.
There are fertilizers that can help you on your quest to ensure your soil has the acidity level you’re desiring. But there are also other household ingredients that can too! Left over coffee grounds are a great one!
Here’s an article I found that talks about this further if you’re interested in learning more!