# Colour-changing Hydrangeas and relative pH

**URL:** <https://boards.straightdope.com/t/colour-changing-hydrangeas-and-relative-ph/244937>\
**Category:** Factual Questions\
**Created:** [May 13, 2004, 12:03pm UTC](https://boards.straightdope.com/t/colour-changing-hydrangeas-and-relative-ph/244937 "2004-05-13T12:03:44Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![GingerOfTheNorth](https://avatars.discourse-cdn.com/v4/letter/g/cdc98d/32.png) [@GingerOfTheNorth](https://boards.straightdope.com/u/GingerOfTheNorth)\
**Post date:** [May 13, 2004, 12:03pm UTC](https://boards.straightdope.com/t/colour-changing-hydrangeas-and-relative-ph/244937/1 "2004-05-13T12:03:44Z")

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The Hydrangea is a new plant to me, and I think that it’s beautiful. I never saw one until I moved East. They puzzle me. My father-in-law informs me that the colour of the flowers depends on the pH of the soil. How is this possible?

I don’t doubt his word, because I’ve seen the different colours and he’s explained to me how to change the relative pH one way (lime, but I can’t remember how to change it the other way), but I just want to know why it happens.

Thank you!

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**Author:** ![Bewildebeest](https://avatars.discourse-cdn.com/v4/letter/b/779978/32.png) [@Bewildebeest](https://boards.straightdope.com/u/Bewildebeest)\
**Post date:** [May 13, 2004, 12:56pm UTC](https://boards.straightdope.com/t/colour-changing-hydrangeas-and-relative-ph/244937/2 "2004-05-13T12:56:08Z")

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> [@GingerOfTheNorth](#):
>
> The Hydrangea is a new plant to me, and I think that it’s beautiful. I never saw one until I moved East. They puzzle me. My father-in-law informs me that the colour of the flowers depends on the pH of the soil. How is this possible?
> 
> I don’t doubt his word, because I’ve seen the different colours and he’s explained to me how to change the relative pH one way (lime, but I can’t remember how to change it the other way), but I just want to know why it happens.
> 
> Thank you!

Any type of acidity will make them blue, but Aluminium Sulphate is generally recommended. I couldn’t find a whole lot about why, but look for ‘hydrangea’ in this link for what I could find.

[http://www.bmi.net/roseguy/redshoot.html](http://www.bmi.net/roseguy/redshoot.html)

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**Author:** ![GingerOfTheNorth](https://avatars.discourse-cdn.com/v4/letter/g/cdc98d/32.png) [@GingerOfTheNorth](https://boards.straightdope.com/u/GingerOfTheNorth)\
**Post date:** [May 13, 2004, 7:47pm UTC](https://boards.straightdope.com/t/colour-changing-hydrangeas-and-relative-ph/244937/3 "2004-05-13T19:47:05Z")

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Anthocyanins. Works for me. Thank you!

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**Author:** ![Scarlett67](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/scarlett67/32/7387_2.png) [@Scarlett67](https://boards.straightdope.com/u/Scarlett67)\
**Post date:** [May 13, 2004, 8:14pm UTC](https://boards.straightdope.com/t/colour-changing-hydrangeas-and-relative-ph/244937/4 "2004-05-13T20:14:08Z")

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The plot of a mystery story I once read involved a hydrangea bush changing color because a gun was buried under it.