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Periodic Graphics

Periodic Graphics: The chemistry of hydrangea color changes

Chemical educator and Compound Interest blogger Andy Brunning illustrates the chemistry behind hydrangeas’ hues

by Andy Brunning, special to C&EN
April 28, 2024 | A version of this story appeared in Volume 102, Issue 13


Infographic on the chemistry of hydrangea color changes.

Anthocyanins, primarily delphinidin-3-glucoside, are the main pigments contributing to color in hydrangeas.

Unlike any other flowers, hydrangeas have sepals whose color is sensitive to soil acidity. The color can be shades of blue, pink, or purple depending on the soil's pH. 

Aluminum ions in the soil, which exist in nontoxic silicates or oxides and are released by lower soil pH, also affect the color.

Hydrangeas take up the soluble aluminum ions, which form a complex with delphinidin-3-glucoside and phenolic copigments in hydrangea sepals. This complex gives the sepals a blue color.

Adding sulfur or aluminum sulfate to acidify soil or adding lime to make soil more alkaline can adjust hydrangea colors.
Credit: Andy Brunning

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References used to create this graphic:

Ito, Takaaki, Dan Aoki, Kazuhiko Fukushima, and Kumi Yoshida. “Direct Mapping of Hydrangea Blue-Complex in Sepal Tissues of Hydrangea macrophylla.” Sci. Rep.(2019). DOI: 10.1038/s41598-019-41968-7.

Schreiber, Henry. “Curious Chemistry Guides Hydrangea Colors.” American Scientist, November–December 2014, 444. DOI: 10.1511/2014.111.444.

Yoshida, Kumi, Kin-ichi Oyama, and Tadao Kondo. “Insight into Chemical Mechanisms of Sepal Color Development and Variation in Hydrangea.” Proc. Jpn. Acad., Ser. B(2021). DOI: 10.2183/pjab.97.003.

A collaboration between C&EN and Andy Brunning, author of the popular graphics blog Compound Interest

To see more of Brunning’s work, go to To see all of C&EN’s Periodic Graphics, visit



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