Question
Hi Marc:

What do I do to my soil (I know I need to add aluminum?) to make my white hydrangeas turn blue.  How do I do this.  Everyone tells me the ph level needs to be such 'n such, or something needs to be added to the soil, but I don't know exactly what to do.  Please advise.

Thanks,

Tori

Answer
I don't know if you can turn WHITE into BLUE, but many gardeners buy a blooming BLUE flowered plant, only to have them turn PINK after they plant them, or PINK/RED ones that turn BLUE/PURPLE after planting...all due to the change in pH of the soil they get stuck into...

Generally, the plant has to already have pigmentation, then the fun begins:  

more acidic = BLUE/PURPLE,
less acidic =  PINK/RED.

More acid? Add Aluminum sulfate.  Less acid? Add lime or superphosphate.  

Also, you have to add these BEFORE the blooms form.  If the flowers are on the plant, its too late.

Maybe, if your WHITE is really a pale shade of BLUE of PINK you may have some luck messing with the pH. If it is an albino variety, I don't think it will work.  

To add to the confusion, I know of at least 5 different sub-species of Hydrangea.

check out this website for more info:
http://www.hydrangeashydrangeas.com/

Regards - Marc