There is no reason to panic, but the plant needs to be taken care of, otherwise problems cannot be avoided.
Reddening of hydrangea leaves is associated with a number of reasons. Most often, it is about improperly selected soil for the plant.
Hydrangea loves slightly acidic soil, but it is initially planted in soil with a pH of 5.
This level is rare in natural conditions, so it may need to be “adjusted” to the norm.
To do this, add ash or water the soil with a solution based on citric acid. A special device is used to accurately measure the acidity of the soil.
The second reason why leaves turn red is related to pruning. It cannot be done during the active phase of vegetation. In this case, sap flow is disrupted.
The color of the hydrangea leaves can change due to pests. But in this case, not the entire leaf turns red, but spots appear. In this case, the plant must be treated with insecticides.