To make the soil more acidic and your hydrangeas blue, add a half cup of garden sulfur around the dirt beneath the hydrangeas.
To make it more alkaline, therefore raising the pH, use ground lime in the soil for pink blooms. You may need to reapply the garden sulfur or lime over the course of several months to see results.
It’s definitely a waiting game. You may not even notice a change until the flowers emerge again next blooming season.
It’s also worth mentioning that not all types of hydrangeas are able to change color. Plants with white flowers do not respond to adjustments in soil chemistry. White blooms will stay white.
And as a final note, avoid messing with the soil pH if you have just planted your hydrangeas into the ground. Wait for them to settle into their environment for a season before trying to change the flower color.
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