For a long-term way to acidify the soil and stimulate beautiful blue hydrangea flowers, sprinkle 1 to 2 tablespoons of elemental sulfur per square foot of soil and mix it into the top few inches.
This method is ideal if you’re looking for a short-term adjustment, but it will need to be reapplied every few weeks. Avoid splashing the leaves to prevent potential damage.
Scatter used coffee grounds around the base of your hydrangeas and gently work them into the topsoil to lower soil pH over time and provide a slight nitrogen boost.