# Gardeners: Hydrangea flower color question **URL:** \ **Category:** Factual Questions\ **Created:** [July 16, 2007, 10:03pm UTC](https://boards.straightdope.com/t/gardeners-hydrangea-flower-color-question/412042 "2007-07-16T22:03:52Z")\ **Posts on this page:** 12\ **Page:** 1
**Author:** ![Athena](https://avatars.discourse-cdn.com/v4/letter/a/35a633/32.png) [@Athena](https://boards.straightdope.com/u/Athena)\ **Post date:** [July 16, 2007, 10:03pm UTC](https://boards.straightdope.com/t/gardeners-hydrangea-flower-color-question/412042/1 "2007-07-16T22:03:52Z")
I’ve wanted a hydrangea forever, and I finally bit the bullet and bought one this spring. I’ve been putting some sort of Miracle Grow brand stuff on 'em that the nursery told me would make the flowers blue (not normal Miracle Grow - something designed to make the pH of the soil correct for the blue flowers.) Indeed, the flowers, tiny though they are, are definitely blue! Light blue, that is. Sort of a bluish lilac, to tell the truth. I want 'em really blue, so I’m determined to up the amount of stuff I put on them. My question for you all is, if I change the pH of the soil, will it affect the current flowers, or just new ones? In other words, at what point in the flower growing cycle does it need the correct pH to produce blue flowers? ---
**Author:** ![Shayna](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/shayna/32/17976_2.png) [@Shayna](https://boards.straightdope.com/u/Shayna)\ **Post date:** [July 16, 2007, 10:16pm UTC](https://boards.straightdope.com/t/gardeners-hydrangea-flower-color-question/412042/2 "2007-07-16T22:16:32Z")
You may find the answers you’re seeking here: [Changing the Color of Hydrangeas](http://www.hydrangeashydrangeas.com/colorchange.html). Lots of Hydrangea Q&As from the [United States National Arboretum website](http://www.usna.usda.gov/Gardens/faqs/hydrangeafaq2.html). ---
**Author:** ![Jackmannii](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jackmannii/32/311_2.png) [@Jackmannii](https://boards.straightdope.com/u/Jackmannii)\ **Post date:** [July 16, 2007, 10:19pm UTC](https://boards.straightdope.com/t/gardeners-hydrangea-flower-color-question/412042/3 "2007-07-16T22:19:19Z")
This may sound obvious, but to get blue flowers you need a hydrangea capable of producing them (if the natural flower color tends to other shades, increasing the soil acidity may not produce true blue blooms). If you have the right variety, adjusting soil pH is probably not going to affect existing blooms, but is more likely to work if the plant is only partway along in the blooming process (i.e. buds just forming). If your soil is already properly acidic (i.e. a pH of 5 to 5.5), you don’t need to do anything else. If it’s too alkaline (a soil test kit will tell you this), you can keep watering with an acidic fertilizer at the recommended rate, or for a longer-term (and safer) remedy, use a soil additive that gradually lowers the pH (like peat moss or coffee grounds). [This site](http://www.gardeners.com/Growing-Blue-Hydrangeas/default/hydrangealp.page) talks about how to get blue hydrangea flowers, and includes the suggested application rate of aluminum sulfate, a compound often used to treat soils in which hydrangeas are growing. Good luck. ---
**Author:** ![Athena](https://avatars.discourse-cdn.com/v4/letter/a/35a633/32.png) [@Athena](https://boards.straightdope.com/u/Athena)\ **Post date:** [July 16, 2007, 11:37pm UTC](https://boards.straightdope.com/t/gardeners-hydrangea-flower-color-question/412042/4 "2007-07-16T23:37:36Z")
Yes, it is a variety that can be really blue. I made sure of that when I bought it. Thanks for the links, **Shayna** and **Jackmannii** , but I read through both of those before posting the question. Maybe I missed something, but nothing really says that existing flowers can change color. They don’t say that they can’t, either. They just seem to skip over that little factoid. So to clarify: I’m not looking for information on HOW to make them blue, I know how already. What I specifically want to know is if I need to wait for new buds to show up to see if my efforts have worked or if I should be seeing the change on the one flower that’s already there. ---
**Author:** ![Shayna](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/shayna/32/17976_2.png) [@Shayna](https://boards.straightdope.com/u/Shayna)\ **Post date:** [July 17, 2007, 12:33am UTC](https://boards.straightdope.com/t/gardeners-hydrangea-flower-color-question/412042/5 "2007-07-17T00:33:39Z")
The best I could find was a posting on the UBC Botanical Gardening website that says (bolding mine): [ > [@](#): > > A standard nursery and home gardening practice is > to add some aluminum sulfate into the soil to turn a > pink Hydrangea into a blue colored one. It may take > 2-3 light applications (1oz) to force the color change. > Use superphosphate to change a blue Hydrangea into > a pink or a red one. Apply superphosphate in liberal > amounts (2oz) during the growing season to keep the > Hydrangeas pink or red also. **The above fertilizers > must be applied well in advance of bloom to achieve > the desired color results.** ]([Why no blue hydrangeas??? | UBC Botanical Garden Forums](http://www.ubcbotanicalgarden.org/forums/showthread.php?t=5071)) And this from the Agriculture department of Texas A&M (bolding mine again): [ > [@](#): > > The color of the bloom can be adjusted. White blooms will always be white, while the blue or pink can be controlled by the pH of the soil (the closer to a balanced pH of 6.5, the lighter the color). **Add agricultural lime in the fall** for deeper pinks or aluminum sulfate for darker blues. ]([http://aggie-horticulture.tamu.edu/county/smith/tips/trees/hydrangea.html](http://aggie-horticulture.tamu.edu/county/smith/tips/trees/hydrangea.html)) So it does seem that you would have needed to plan in advance to achieve your blue flowers. ---
**Author:** ![Harmonious\_Discord](https://avatars.discourse-cdn.com/v4/letter/h/74df32/32.png) [@Harmonious\_Discord](https://boards.straightdope.com/u/Harmonious_Discord)\ **Post date:** [July 17, 2007, 12:51am UTC](https://boards.straightdope.com/t/gardeners-hydrangea-flower-color-question/412042/6 "2007-07-17T00:51:38Z")
It sounds like your not at the point of full heads. I would expect them to darken as they reach full size. You may wish to amend the soil with aluminium sulphate. That is what the Miracle Grow has in it. You should really get a ph testing kit and check what the soil is currently at. [http://www.home-herb-garden.com/hydrangeas.html](http://www.home-herb-garden.com/hydrangeas.html) Excerpt from linked site: Plant age also seems to affect flower colour and some varieties may take 2-3 seasons after planting to settle into the final stable colour. Adding aluminium sulphate to the soil prior to budding to produce blue flowers; or by liming or adding quantities of superphospate to the soil to produce pink ones may control the flower colours. However it requires large quantities at frequent intervals to control the colour. ---
**Author:** ![Savannah](https://avatars.discourse-cdn.com/v4/letter/s/b3f665/32.png) [@Savannah](https://boards.straightdope.com/u/Savannah)\ **Post date:** [July 17, 2007, 12:59am UTC](https://boards.straightdope.com/t/gardeners-hydrangea-flower-color-question/412042/7 "2007-07-17T00:59:32Z")
This is absolutely not helpful at all, but I love the hydrangaes that are pink on one side of the bush, blue on the other, and have a luscious, delicate blend of pink and blue and violet in the middle. So very pretty. ---
**Author:** ![Athena](https://avatars.discourse-cdn.com/v4/letter/a/35a633/32.png) [@Athena](https://boards.straightdope.com/u/Athena)\ **Post date:** [July 17, 2007, 12:57pm UTC](https://boards.straightdope.com/t/gardeners-hydrangea-flower-color-question/412042/8 "2007-07-17T12:57:07Z")
[QUOTE=Savannah] This is absolutely not helpful at all, but I love the hydrangaes that are pink on one side of the bush, blue on the other, and have a luscious, delicate blend of pink and blue and violet in the middle. So very pretty. [/QUOTE] Wow, I didn’t even know you could do that! I wonder how you get THAT to happen?!? ---
**Author:** ![Zsofia](https://avatars.discourse-cdn.com/v4/letter/z/7bcc69/32.png) [@Zsofia](https://boards.straightdope.com/u/Zsofia)\ **Post date:** [July 17, 2007, 1:07pm UTC](https://boards.straightdope.com/t/gardeners-hydrangea-flower-color-question/412042/9 "2007-07-17T13:07:48Z")
Generally you just happened to plant it where your soil changes pH. Or it’s a large bush and you dope both sides. ---
**Author:** ![Harmonious\_Discord](https://avatars.discourse-cdn.com/v4/letter/h/74df32/32.png) [@Harmonious\_Discord](https://boards.straightdope.com/u/Harmonious_Discord)\ **Post date:** [July 17, 2007, 2:10pm UTC](https://boards.straightdope.com/t/gardeners-hydrangea-flower-color-question/412042/10 "2007-07-17T14:10:17Z")
There are some that bloom blue and change to a pink as they get old. ---
**Author:** ![Dinsdale](https://avatars.discourse-cdn.com/v4/letter/d/97f17d/32.png) [@Dinsdale](https://boards.straightdope.com/u/Dinsdale)\ **Post date:** [July 17, 2007, 2:11pm UTC](https://boards.straightdope.com/t/gardeners-hydrangea-flower-color-question/412042/11 "2007-07-17T14:11:40Z")
Not responsive, but my annabelles and oakleafs are doing great, but I have one climber that has refused to bloom for close to 10 years. Appears healthier than anything, but nary a bloom. Crazy. Soild and sun/shade should be fine. Oh well, not losing any sleep over it and, like I said, the foliage is strong and attractive. ---
**Author:** ![susan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/susan/32/17537_2.png) [@susan](https://boards.straightdope.com/u/susan)\ **Post date:** [July 17, 2007, 6:44pm UTC](https://boards.straightdope.com/t/gardeners-hydrangea-flower-color-question/412042/12 "2007-07-17T18:44:22Z")
My experience is that anything you do this year will affect next year’s blooms. Be sure you follow pruning advice. My hydrangeas are a light blue due to the pH of my natural soil. I can get them a deep, almost purple-blue by pushing the pH further artificially. Soil I truck in from my garden center tends to be a lot less acidic, which I learned one year from its affects on the hydrangea color when I built up some beds.