02/02/2022
You can change a hydrangea's color by altering the pH level of the soil.
A more alkaline soil will result in pinker blooms, while more acidity will produce blue blooms. To coax your plant to the blue side, add more organic matter to your soil, like egg shells and coffee grounds (though the acidity in used coffee grounds can vary greatly, so you might try a high-acid fertilizer, too). The change won't happen overnight, but eventually you should succeed in manipulating your soil's pH level.