Some gardeners report success in turning their hydrangeas blue by applying coffee groundsto the soil. The coffee grounds make the soil more acidic, allowing the hydrangea to more easily absorb aluminum. In addition, fruit peels, lawn clippings, peat moss and pine needles, are thought to have a similar effect.

The easiest way to turn hydrangeas blue is to apply a special slow-release blueing formula product to the soil around the base of the plant. These granular products generally contain aluminum and sulfur (although not always), and are easier to apply than aluminum sulfate.

To make your Hydrangeas blue, you first need to test your soil to determine the pH level. For blue blooms, the soil needs to be acidic, with a pH level at or below 5.5. You can use simple additives to change the soil’s pH. To keep your Hydrangea blooms blue, simply monitor the pH and adjust it as needed.