Blue (pH of 4.5 to 5.5)
The pH of the soil needs to be low, which you can do by adding aluminum sulfate or organic matter like coffee grounds or vegetable peels and grass clippings, according to www.hydrangeashydrangeas.com.
Purple (pH of 5.5 to 6.0)
Some cultivars are reliably purple, Bartlett said, with Merrit supreme being one of her top five favorites.
Pink (pH of 6.2 to 7.0 )
Add lime; according to www.flowersandbulbs.com, a pH of about 6.0 to 6.2 will produce a nice pink, but if you go above 6.4 your plant may have an iron deficiency.
They just stay one color — white. But no matter what color you want, it’s a good year for them overall. “This is going to be one of the best seasons for hydrangea,” Bartlett said. “It was a nice steady cold this winter, one of the best seasons I’ve ever seen.”
Hydrangeas can be found in white, pink, purple and blue — and shades in between. But where do those colors come from?
Underground, in the soil.
Depending on its pH, the soil will tell you if your flowers will be blue, pink, purple or other variations. And there are ways to change the color of your hydrangea if you are hoping for a deep pink or bright blue.
“It’s not hard; the problem is you have to do it early in the season,” Lisa Bartlett of the American Hydrangea Society, which is based in Atlanta. The organization has about 350 members.
“You do it when the buds are super tight and when they are forming,” she said. “To make them blue it’s aluminum sulfate, and to make them pink it’s lime.”
Aluminum sulfate comes in powdered and liquid forms, although Bartlett said it’s the liquid form that’s easier for the plant to pick up.
Blue hydrangeas come from soil with a low pH, ranging from about 4.5 to 5.5. Purple grows in about 5.5 to 6.5, and pink can be found in a pH of 6.0 to 7.0. So, blue hydrangeas grow in a highly acid soil and pink hydrangeas are produced in a neutral or slightly acid soil.
“I just think it’s one of those very comfortable plants that remind us of being with our grandparents, being with our mothers,” she said. “... it’s the first plant people see in a landscape, I think. It’s a nice, sweet plant.”