[agla]

Aluminum sulfate turns those that vary to blue. Lime turns them pink.

I believe that it isactually the Al that affects the color, but lack of acidity binds up the aluminum. We have naturally high amounts of Al here and acidic rain, so we usually don't need an effort to get some really nice blues.

Not all hydrangeas do this.

Some guys put a little lime and a little Aluminum sulfate in patches around the plants to get them to vary on the same plant.