Acidic soils cause hydrangeas to bloom blue (soil pH below 5.5). You can apply aluminum sulfate or sulfur to lower soil pH (broadcast half a cup of wettable sulfur per 10 square feet and water in). To gradually change flower color from pink to blue, broadcast half a cup of wettable sulfur per 10 square feet and water it in.
It’s even better if you can drench the soil. For example, dissolve one tablespoon of aluminum sulfate in one gallon of water, and then drench the soil around the plant in the spring. (Avoid the leaves, and get at soil level).
Acidic soils cause hydrangeas to bloom blue (soil pH below 5.5). You can apply aluminum sulfate or sulfur to lower soil pH (broadcast half a cup of wettable sulfur per 10 square feet and water in). To gradually change flower color from pink to blue, broadcast half a cup of wettable sulfur per 10 square feet and water it in.
It’s even better if you can drench the soil. For example, dissolve one tablespoon of aluminum sulfate in one gallon of water, and then drench the soil around the plant in the spring. (Avoid the leaves, and get at soil level).