It appears that you can get blue Hydrangeas by adding aluminum.
Sky-blue Hydrangeas
July 7, 2010
Neighborly Roses
July 3, 2010
Alert readers may recognize this as a source of an early banner from this site.
Hydrangeas
July 2, 2010
A quick search shows that it’s possible to change hydrangeas from pink to blue and vice versa just by managing the soil’s pH and aluminum content.
sky-blue pinks … Yoshino cherry tree
June 30, 2010
Hello world!
June 14, 2010