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Can You Turn Your Hydrangea Flowers Blue With Just Aluminum Foil?
By PAMELA SIEGEL
Aluminum plays 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.
Providing your hydrangeas with aluminum sulfate is a bit more involved than burying foil in the dirt, but with some patience, it’s still quite easy to accomplish.
Only bigleaf and mountain hydrangeas can change color with aluminum sulfate. Darker reddish pink, deep blue, and white blooms won’t be affected by soil additives.
For this hack, mix 1 tablespoon of aluminum sulfate with 1 gallon of water and soak the plant’s base once a month for three months, preferably in spring or the beginning of summer.
You can also wait until fall and sprinkle ½ cup of wettable sulfur over every 10 square feet of soil, then water the area. It could take up to a year for the color to change.
This hack works because of how aluminum sulfate affects soil pH. It decreases the soil pH, which is what causes hydrangea plants to turn blue.