Hydrangea bloom not coloring

I have a Nikko hydrangea, planted a couple of months ago, that has grown quite a bit and looks very healthy. I purchased it from a nursery with one mophead already on it but it was still green. The mophead has also grown but hasn't colored at all.
Another mophead is forming but is white. Its planted in shade with patchy morning sunlight for a few hours and has been kept well-watered. My other hydrangeas (not Nikkos) are blooming away beautifully. Any guesses as to why the flowers aren't coloring?
-- Tara
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Oops, I'm in lower zone 8
-- Tara
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Hon sounds like it was mis-labeled at the nursery. It should be either blue or pink depending on soil pH. Preferably Blue for a Nikko. Sorry. Take it back.
Elaine in Ga Zone 7b

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Thanks Elaine. I just went out and checked it again (I probably look in on it 10x a day) and the new mophead that's trying to form is turning from whitish-green to pink. The huge mophead that's been on the plant for months is still green though, like the way they come in as new growth, before they get their color.
I don't mind what color it ends up being as I have both blues and pinks but I worry that a) the uncolored bloom is a dud and should be snipped and/or b) the plant needs more sun.
I have found websites that say Nikkos like sun to partial shade and others that say medium shade to little sun. My other hydrangeas wilted terribly until I moved them to primary shade but maybe this one is different?
-- Tara
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Tara my Nikko is in mostly shade with some dappled sun in the morning. I have a woodland garden. It is at the base of a pine tree. Hope this helps. I would say medium shade to little sun. They don't like sun for very long and lord knows it gets hot in GA.
Elaine in Ga Zone 7b

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The colour of the blooms is determined by the soil's pH or something, and you can swap over their colour by adding the appropriate mineral to the soil. The actual brilliance of the colour is determined largely by the hydrangea's genes I guess.
So I'm wondering whether your new acquisition is planted in soil that is different from what the others are growing in? Maybe there is a lot of lime or cement waste or something in its soil? You haven't mentioned adding blueing (or pinking) compound to its soil, have you tried that? I think any mushroom compost added to the soil would have made it a bit acid. -- John Savage (my news address is not valid for email)
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As I stated above soil pH determines the color. Alkaline for blue, acid for pink but they start out green until they mature. The plant itself tends to like acid soil which is what we have down here but my nikko (2yrs old) still is blue so far just maybe not a brilliant blue. Hopefully that will not change.
Elaine in Ga Zone 7b
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Without consulting a reference, I'd say you have that 'round the wrong way. I seem to remember hydrangeas being the opposite to litmus; hydrangeas are blue in acid and pink in alkali I think.
(Actually it's not that straightforward, as I recall a science teacher winning a science award for determining what it *really* is that changes the hydrangea's colour from pink to blue or back again, but roughly speaking using pH is good enough, but you probably know that.)
--
John Savage (my news address is not valid for email)

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The acidic soil permits the aluminum in the soil to be taken up which is what makes the flowers blue. Maybe with acidic soil and no aluminum they would be white, I don' t know.
Aluminum is toxic to many plants such as azaleas and rhododendrons, so don't think that aluminum sulfate is good for acidifying the soil for all plants. But, it will make most mophead hydrangeas bloom blue.
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http://www.flowersbulbs.com/manipulatecolor.cfm
Here is a reference for pH and coloring. I did have it backwards. Sorry, thanks John.
pH of 4.5-----deep blue----acid
pH of 7.0----deep pink----alkaline
Aluminum in the soil is the element responsible.
*note that white hydrangeas are not altered at all. white stays white.
Elaine in Ga Zone 7b
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Actually a pH of 7 is neutral, perfectly neutral.
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In the hydrangea "world" a pH of 7 is enough Alkaline for pink. Nickpicker

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No, not a nitpicker, he's correct. 7 is not alkaline at all. Look it up.
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Ann, gardening in Zone 6a
South of Boston, Massachusetts
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Yes Ann theoretically 7 is neutral. In this discussion however, if you will read from the beginning, is in regards to the proper pH for the color of hydrangeas. 7 is the proper pH for pink and is considered alkaline enough to produce that color. See the link I provided on the subject. http://www.flowersbulbs.com/manipulatecolor.cfm
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What Stephen said. Not encouraging a misconception is all that's being avoided here.
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In the hydrangea "world" a pH of 7 is neutral enough for pink.
Just as rain water is not weak lemonade, a pH of 7 is not alkaline.

Not theoretically, by definition. By definition alkaline means:
"Having the properties of an alkali; having a pH greater than 7."
Obviously a pH of 7 doesn't qualify. The website you are quoting is making a common mistake of equating less acidic with more alkaline and that is not true.
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