Which flower changes color based on soil pH?

The flower known for changing color according to soil pH is the hydrangea, particularly cultivars of Hydrangea macrophylla and Hydrangea serrata. Acidic soil generally produces blue to purple flowers, while alkaline soil tends to produce pink or red ones.

The chemistry involves aluminum ions. In acidic soil, aluminum is more soluble and can be absorbed by the plant. Inside the flower’s tissues, aluminum interacts with anthocyanin pigments, shifting the visible color toward blue. In alkaline soil, aluminum is more tightly bound in the soil, so the flowers usually remain pink or reddish.

The effect is not universal across every hydrangea. Many species naturally produce white flowers, and white cultivars generally cannot be turned blue or pink simply by changing soil acidity because they lack the relevant pigments. Genetics, available aluminum, and the plant’s age also influence the final shade.

Hydrangeas are native to Asia and the Americas, with especially high species diversity in East Asia. Gardeners can alter soil conditions gradually, but color changes may take a growing season and are most reliable in suitable bigleaf hydrangea cultivars.