Why do hydrangeas die?

Hydrangeas may die due to improper care, such as overwatering, by exposure to extremely cold temperatures and by infection with disease such as root rot. Some hydrangeas are more susceptible to disease and changes in environmental conditions than others are. Generally, hydrangeas enjoy plenty of sunlight while only big leaf hydrangeas are vulnerable to damage from environmental factors such as freezes.

Hydrangeas are also susceptible to certain diseases and predation from insects such as aphids and Japanese beetles. Root rot, particularly Armillaria root rot, is a primary killer of oakleaf hydrangeas. Plants afflicted with this root rot may wilt and eventually die, as they become easily overwatered. This disease can be prevented by potting hydrangeas in soils that drain excess moisture.