Hi, I just ordered my mom some daylilies and because they won't ship until the fall I was given the choice of 2 free plants (Autumn Ridge Nursery). I read the list to her and she chose blue hydrangeas. So I just did some poking around on the web and it said that to keep them blue you need to keep the soil acid. Sorry, I don't know how to make a link so I just copied and pasted:

"If you're growing Hydrangea Marcrophylla (French Hydrangea) you can turn it from pink to blue by lowering the pH level of your soil. The color is determined by the amount of aluminum available to the plant. Add 3 to 4 tablespoons of aluminum sulfate to a gallon of water. Apply it 2 times, 2 weeks apart, for 4 to 6 months prior to blooming. You can also add coffee grounds, eggshells or ground-up citrus peel to the soil. You're shooting for a pH of 5-6.

On a similar note, blue hydrangeas can be changed to pink by adding 3-8 cups (depending on the size of the plant) of dolomic lime around the base of the hydrangea. Do this 2 or 3 times between the blooming seasons. As an alternative, you can also try a bit of superphosphate around the base of the plant. Shoot for a pH of 6.8-7.2.

The color change doesn't happen overnight so be patient. It can take as long as a year or two to see the results. The white varieties of hydrangeas (such as PeeGee, Silver Leaf, Hills of Snow, etc.) cannot be changed. They remain while regardless of tampering with the pH of the soil."

Hope this helps. I'm going to print it out and send it to my mom when they ship her plants in the fall.

Kimberly