Hydrangeas remain favorites with gardeners who love big, colorful blooms as part of a yard’s landscaping or in cut arrangements inside the home. And you can even switch up the color to your liking — yes, a couple of varieties can change color from pink to blue under the right conditions. But is one of these conditions adding aluminum foil to the soil near your plant? Despite what some people might say online, the answer is no.
Aluminum does play a part in making hydrangeas change their color to blue, but the helpful soil additive that encourages this neat trick is aluminum sulfate rather than aluminum foil. Supplying your plant with aluminum sulfate is a bit more involved than burying foil in the dirt, but it’s still quite easy to accomplish as you’re routinely caring for your garden. One of the hardest parts of the process, though, is mustering up some patience.
Changing hydrangeas from pink to blue with aluminum sulfate
Keep in mind that not all types of hydrangeas can change color from pink to blue. If you have varieties other than bigleaf or mountain hydrangeas, no amount of aluminum sulfate is going to change the color. Darker reddish pink and very deep blue flowers, along with white blooms, will not be affected by soil additives.
If you have the right variety, however, you can give this hack a go. Just mix 1 tablespoon of aluminum sulfate with 1 gallon of water and soak the base of the plant once each month for three months. The best time to do this is in the springtime or the beginning of the summer months in your area. You can also wait till the fall and sprinkle 1/2 cup of wettable sulfur over every 10 square feet of soil where your hydrangeas are growing, then water the area so the additive seeps down into the ground. This is where patience comes into play. It can take months or even up to a year for the color change to take place.
Wondering how you can change them back to pink again if you decide you like that better? The same process is applied in the spring mixing 1 tablespoon of hydrated lime with one gallon of water (instead of aluminum sulfate). Or, you can add 1 cup of dolomitic lime over 10 square feet of ground before watering your plants.
The reaction that causes hydrangeas to change colors
Now you know that you can indeed change the color of hydrangeas from pink to blue and back to pink again if you like. You probably suspect there’s some science behind what makes this happen, and you’d be right; it’s all in the soil chemistry. More specifically, it has to do with the pH level of the soil. You can have your soil tested to find out the pH level, or you can simply plant a hydrangea in your garden and see what happens.
Hydrangeas turn blue when the soil is more acidic (about pH 5.5 or less) and pink when it’s more alkaline (around pH 7 or more). Thus, adding aluminum sulfate to the dirt decreases the pH, and adding lime increases it. At the end of the day, just remember that aluminum sulfate produces blue flowers, and you never have to wonder about placing foreign objects like aluminum foil near your hydrangeas again.
