Aluminium sulfate is sometimes used to reduce the pH of garden soil, as it hydrolyzes to form the aluminium hydroxide precipitate and a dilute sulfuric acid solution. An example of what changing the pH level of soil can do to plants is visible when looking at "Hydrangea macrophylla". The gardener can add aluminium sulfate to the soil to reduce the pH which in turn will result in the flowers of the "Hydrangea" turning a different color (blue). The aluminium is what makes the flowers blue; at a higher pH, the aluminium is not available to the plant.