Gardens often use this as a soil amendment to "turn their hydrangea's blue". The color of your hydrangea (pink or blue) is often affected by your soil's acid level. Espoma Soil Acidifier organically lowers the soil's pH for growth of acid-loving plants through the use of garden sulfur which is an all natural mineral. This product is safer than Aluminium Sulfate which might be an alternative produce used to achieve similar results.