How Long Does It Take To Turn A Pink Hydrangea Blue?

Many people ask me how to turn their pink hydrangeas blue⁠—a lot more than those who ask how to turn a blue hydrangea pink. The South loves the blues, I guess. I answer just like everyone else, with the caveat that it takes a lot of patience.

The flower color of a French, or bigleaf hydrangea (Hydrangea macrophylla), depends on whether the soil is acidic (below pH 7.0) or alkaline (above pH 7.0). Strongly acidic soil of 6.5 or below produces blue flowers. Alkaline soil has pink or red flowers, and near-neutral soil of pH 6.5 to 7 gives you purple flowers or a mixture of blue and pink blooms. White hydrangeas won't change color at all.

How To Turn Hydrangeas Blue

How do you change the soil pH? To make it more acidic, you add sulfur. To make it more alkaline, add ground limestone or lime. Easy-peasy, right? Not so fast.

Some hydrangeas change color easily. The original 'Endless Summer' is one. A potted blooming pink variety planted in strongly acidic soil will likely bear bright-blue flowers the following year. A similar flower growing in near-neutral soil will feature half of its flowers as blue and half as pink.

The 'L.A. Dreamin' hydrangea is another matter. L.A. stands for 'Lindsey Anne,' the name of the breeder's daughter. This variety features big multi-colored blooms in blue, purple, and pink smothered it. The flowers on this four-foot shrub bloom from early summer until fall. It also blooms on both old and new growth, so even if winter kills the flower buds or you cut them off by pruning at the wrong time (in fall and winter), you still get blooms on new stems.

'L.A.' Dreamin' performs well in a big container. The flowers will emerge bright pink, slowly aging to nearly red, and last for months. For color variation, try Espoma Organic Soil Acidifier, which contains 30% sulfur and is safer than potentially toxic aluminum sulfate. The label recommends sprinkling 1 1/4 cups around each new plant or 2 1/2 cups around established plants. 

Potted plants get one tablespoon for every four inches of pot diameter. Spread the sulfur evenly out to the widest branches and water it in. Repeat at 60-day intervals until you get the color you want. A pH of 5.5 should result in violet-blue blooms, while 4.5 will result in a deep blue. A soil pH of 5.0 will cause flowers to bloom in a more muted blue.

Hydrangeas Take Their Time

Large hydrangea plants can take months to convert their color, so you might not see the results until next year's bloom. Sometimes you'll see some flowers change color and others not, so be patient and amend the soil as needed.

WATCH: Easy Ways to Change Hydrangea Colors

Troubleshooting Hydrangea Color Variations

Consider the following issues if you need help achieving the color variation in the hydrangea you planted. Growing the hydrangea near concrete might make turning flowers blue more challenging. One more factor that people seldom consider is their water quality and its pH. Hard water contains many dissolved minerals like calcium and magnesium, making it alkaline. Soft water contains few minerals and is acid. So, changing the flower color from pink to blue will be a long and ongoing process if you're watering your hydrangea with hard water. Use rainwater instead whenever you can. By next year you could be well on your way to bright blue hydrangeas.