One of the best features of hydrangeas is their color—pink or blue—and it’s a feature that’s entirely controllable by you.
First, hydrangea bloom color is determined by the pH level of the soil. An acidic soil has a pH level of less than 7, while an alkaline soil has a pH of more than 7. pH level—the measure of how much calcium is in the soil—are important factors in planting because depending on the level, available nutrients will differ. As a rule of thumb, acidic soils tend to populate moist climates, while alkaline tends to populate dry climates.
Pink-colored flowers must be grown in acidic soil without aluminum. A lot of soils contain aluminum, so it’s important to add a fertilizer that contains phosphorus to your soil to help eliminate the metal traces. After you do that, you’ll need to add calcium or limestone (or a combination of both) to the soil as necessary to raise the pH level, but only to the 6.0-6.5 range, as anything higher may result in iron deficiency within the plant.
To change your flowers to blue, add a ½ to 1 cup of aluminum sulfate to the soil at planting time. Keep track of your pH level, because you want to lower it to around 5.5 (it can go as low as 5.2). You can also add things such as grass clippings, coffee grounds and fruit/vegetable peels to help lower pH levels. Fertilizer rich in potassium will also aid in this process.
Changing the color of the blooms on your hydrangea is especially easy to do if you grow them in containers or on the patio. Regardless of the way you choose to do it or wherever you decide to grow them, your hydrangeas are sure to brighten your garden, whether they’re pink or blue.