How Long Does It Take To Turn a Pink Hydrangea Blue?
Many people ask me how to turn their pink hydrangea 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 aka bigleaf hydrangea (Hydrangea macrophylla) depends on whether the soil is acid (below pH 7.0) or alkaline (above pH 7.0). Strongly acid soil of 6.5 or below produces blue flowers, alkaline soil produces pink or red flowers, and near-neutral soil of pH 6.5 to 7 gives you purple flowers or a mixture of blue blooms and pink ones. White hydrangeas won't change color at all.
How to Turn Hydrangeas Blue
How do you change the soil pH? To make it more acid, you add sulfur. To make it more alkaline, you add ground limestone, otherwise known as lime. Easy-peasy, right? Not so fast.
Some hydrangeas change color easily. The original 'Endless Summer' is one. I bought one that was blooming pink in the pot, planted it into my strongly acid soil, and the next year it bore bright-blue flowers. In a neighbor's yard with near-neutral soil, half of its flowers were blue and half were pink.
My 'L.A. Dreamin' hydrangea (see the photo above) is another matter. L.A. stands for 'Lindsey Anne,' the name of the breeder's daughter, and it's also sold under that name. I was smitten the first time I saw it out in California. Big multi-colored blooms in blue, purple, and pink smothered it. The flowers on this 4-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' performed admirably for me in a big container. The flowers emerged bright pink, slowly aged to nearly red, and lasted for months. I ended up drying the last flowers indoors. My only quibble is I wanted a little more blue, a little more purple.
I turned to 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 1 tablespoon for every 4 inches of pot diameter. Spread the sulfur evenly all the way 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. My hydrangea just received its third application and I'm still waiting for the first sign of blue. I think it will happen. I'll just have to take the same advice I so often dole out to you. Be patient.
WATCH: Easy Ways To Change Hydrangea Colors
If you're stymied, consider where you've planted your hydrangea. Is it growing near concrete? Unfortunately, the lime in that concrete can make turning flowers blue a lot tougher. One more factor that people seldom consider is their water quality and its pH. Hard water contains lots of dissolved minerals like calcium and magnesium and is alkaline. Soft water contains few minerals and is acid. So if you're watering your hydrangea with hard water, changing the flower color from pink to blue is going to be a longer and ongoing process. Use rainwater instead whenever you can. By next year you could be well on your way to bright blue hydrangeas.