How do I change the pH in...

It’s easy to modify your soil’s pH. Start with the Hydrangea macrophylla variety. Soil that is on the acid side (pH between 4.5 and 5.5) will produce blue hydrangeas. Once established, you must fertilize them yearly with an acid fertilizer according to the package directions. When you plant initially, modify the soil with two pounds of sulfur and peat moss. If you want pink to light red hydrangeas, the soil needs to be neutral to alkaline, with a pH of 6.5 to 7.5. Add ground limestone only around the plant to make the blossoms pink. A pH above 7.5 will result in poor growth.