Final answer:
The coloration of hydrangea flowers is largely determined by the soil's acidity, which affects the solubility of aluminum — a key element interacting with pigments to produce color in the flowers.
Step-by-step explanation:
The coloration of hydrangea flowers is influenced by the acidity of the soil in which they are planted. Hydrangea macrophylla is a species where flowers can display different colors based on soil conditions—a phenomenon rooted in soil chemistry. When the soil is more acidic, aluminum becomes more soluble and is absorbed more easily by the plants. This results in blue hydrangea flowers due to the interaction between Al ions and the anthocyanin pigments. Conversely, in more basic (alkaline) conditions where aluminum is less soluble, hydrangea flowers tend to be red.
Gardeners can manipulate this process by altering the pH of the soil, thereby adjusting the flower color. This is an application of Le Chatelier's principle, where changing the acidity affects the equilibrium of aluminum solubility, which in turn affects the flower coloration.