Hydrangeas are beloved for their large, beautiful blooms—and even more exciting, some varieties can actually change color depending on the pH level of your soil! If you’ve ever wondered why your neighbor’s hydrangeas are a deep blue while yours are bright pink, the answer lies in the chemistry of the soil.
Why Do Hydrangeas Change Color?
Not all hydrangeas change color, but Hydrangea macrophylla—commonly known as bigleaf hydrangea—can produce different colored flowers depending on soil pH. The pH level affects how aluminum in the soil is absorbed by the plant. Acidic soil (pH below 6) allows the plant to absorb more aluminum, resulting in blue blooms. Alkaline soil (pH above 7) blocks aluminum absorption, giving you pink flowers.
How to Turn Hydrangeas Blue
If you’re dreaming of blue hydrangeas, you’ll need to make your soil more acidic. You can lower the pH by adding:
- Aluminum sulfate (available at garden centers)
- Organic materials like coffee grounds, pine needles, or peat moss
Apply these amendments around the base of the plant and water deeply. Be patient—it may take a few weeks or even an entire season to see noticeable changes in flower color.
How to Turn Hydrangeas Pink
To shift your blooms to pink, the goal is to raise the soil pH and reduce aluminum availability. Try adding:
- Garden lime (dolomitic lime works well)
- Wood ash in small amounts
Test your soil first so you don’t overshoot the target pH. Remember, changing flower color isn’t instant—it’s a gradual process that requires consistent soil conditions.
What About White Hydrangeas?
White hydrangea varieties (like Hydrangea arborescens) usually remain white, regardless of pH. Their color is not affected by soil chemistry.
Final Tips
To control bloom color effectively, use a soil pH test kit regularly. Make adjustments slowly and gently over time to avoid shocking your plants. With a little effort, you can create the hydrangea hue of your choice—and even experiment with having multiple colors in one garden bed!
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