Hydrangea care: diagnosing blackening or dried leaves

Gardeners facing blackening or dried hydrangea leaves in late summer and autumn are advised to diagnose the cause before pruning or removing the plants. Common issues include frost damage, fungal infections like powdery mildew, and water-related stress.

Frost typically causes uniform, dark brown or black leaves that soften and then dry out. Fungal issues such as powdery mildew often present as a white powdery coating followed by brown necrosis, while sooty mold caused by scale insects appears as a black residue that can be wiped off. Soil conditions also play a role; heavy, waterlogged soil can lead to root oxygen deprivation and risks like Phytophthora.

In cases where plants appear scorched or dried out due to heat, it is often a defense mechanism against hydric stress rather than direct heat damage. To determine if a plant is still alive, gardeners can perform a quick bark test: scratching a small area of the stem to check if the underlying wood is still green and moist.