Hydrangeas are one of the most beautiful, abundant perennials you could have in your garden.  They seem happy all the time with their big, plentiful green leaves and the fluffy flowers that bring sunshine to any corner.  They can also be allusive and difficult at times, when they don't get what they need.  One gardener asks:
 
"My question concerns Hydrangeas.  I love the blue color, however, soon after I plant them, they are no longer blue but green to pink.  What should I do?"

The answer is "it's all in your soil pH."  Hydrangeas are acid loving plants and they require acidic soil in order to maintain their color.  You can change the Ph of your soil over time to better accommodate your acid loving plants.  There are a few solutions I can offer you:

Iron (ferrous) sulfate  - will help correct soil pH.  It is often used for treating Iron Chlorosis, which is the yellowing of leaves due to mineral deficiencies.  Bonide makes an iron sulfate in granular form.  You can find Bonide Iron Sulfate at http://homeharvest.com/soilconditionerspH.htm.

Aluminum Sulfate - is another way to correct soil pH.  Either this or Iron sulfate can be used to keep your hydrangeas blue. 

Shrubs Alive - a product from Gardens Alive can be added as a regular fertilizer to your acid loving plants, including hydrangeas on a seasonal basis to keep plants strong and soil acidic.  Click on the link and scroll down to Shrubs Alive:

 

Finally, I have been told that you can bury a few iron nails in the soil around your plants and they will leech into the soil over time, changing the pH.  Give it a try and report back on your findings. 


Here is a supplemental article that will go into more detail about hydrangeas and maintaining their color: http://www.hydrangeashydrangeas.com/colorchange.html