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#51061 May 24th, 2007 at 12:00 PM
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Hi all

I recently bought 2 beautiful blue hydrangea plants. The tab in the soil said part to full shade, so I put them in 2 nice pots and put them in the shade on my front porch. (It gets about 3 hours of sun a day.) But over the last couple of weeks, the leaves have turned from blue to green. I did some google searches and it says you can force them blue again by adding aluminum sulfate, but I can't find anywhere HOW you add it, WHEN you add it, or how much of it you add. Is anyone here familiar?

NYDeb #51099 May 24th, 2007 at 12:52 PM
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Dear NYDeb I found this great advice from hydrangeashydrangeas.com. I think it says all you need to know!:
To obtain a blue hydrangea, aluminum must be present in the soil. To ensure that aluminum is present, aluminum sulfate may be added to the soil around the hydrangeas.

Authorities recommend that a solution of 1/2 oz (1 Tbsp) aluminum sulfate per gallon of water be applied to plants (which are at least 2-3 years old) throughout the growing season. Important: Water plants well in advance of application and put solution on cautiously, as too much can burn the roots.

To make the aluminum available to the plant, the pH of the soil should be low (5.2-5.5). Adding aluminum sulfate will tend to lower the pH of the soil. Another method for lowering the pH is to add organic matter to the soil such as coffee grounds, fruit and vegetable peels, grass clippings etc.

If the soil naturally contains aluminum and is acid (low pH) the color of the hydrangea will automatically tend toward shades of blue and/or purple.

The choice of fertilzer will also affect the color change. A fertilizer low in phosphorus and high in potassium is helpful in producing a good blue color(25/5/30 is good. Potassium is the last number). Superphosphates and bone meal should be avoided when trying to produce blue.

After stating this with much certainty, I hasten to add that it is virtually impossible to turn a hydrangea blue for any length of time if it is planted in soil with no aluminum and that is highly alkaline (chalky). One would have to be very diligent in keeping the soil properly conditioned as stated above.

Perhaps the best idea for growing blue hydrangeas in an area with alkaline soil would be to grow them in very large pots using lots of compost to bring the pH down. The above suggestions for bluing would also work for a potted plant. Reduce the strength of the Aluminum sulfate to 1/4 oz per gallon of water. In a pot, it will be much easier to control the requirements for bluing.

One last suggestions for those who are serious about this process. It is important to have your water tested so that it will not "contaminate" the soil that you have so rigorously balanced. The pH of the water should not be higher than 5.6.

Planting hydrangeas near a concrete foundation or sidewalk will often affect the color since the pH of the soil may be raised considerably by lime leaching out of these structures, making it difficult to obtain blue.

starfish #51136 May 24th, 2007 at 03:15 PM
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Perhaps it was just a misprint, but you said the "leaves" turned from blue to green, not the flowers. Did you mean the flowers? Many hydrangea blooms will change color as they age. My white one eventually turns pink as the flowers age. Also, my Blue Nicco starts off green and turns blue.


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alankhart #51148 May 24th, 2007 at 03:41 PM
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Ugh (*head slap*) yes... I meant the blooms turned green.

starfish #51150 May 24th, 2007 at 03:46 PM
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Thank you starfish, that's exactly what I needed to know!

NYDeb #51170 May 24th, 2007 at 05:04 PM
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Hydrangea sepals tend to change colors as they age. Sometimes the color fades (from dark pink to a lighter shade of pink), other times it changes more (as in white to pink; or pink to green to brown). It depends on what variety one has. You will also notice that sepals sometimes turn upside down or downside up, whichever way you want to describe it. Acidifying the soil will not reverse this fading process though.

NYDeb #51507 May 25th, 2007 at 09:29 AM
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NYdeb - I hope they grow as well as mine! About 15 years ago I planted pink-flowering ones out back under my kitchen window and they still brighten up the view of the garden all summer long!


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