The Q&A Archives: hydrangea disease

Question: Hydrangeas do very well for me but then they develop black spots all over the leaves. What causes this? Is it a fungus?

Answer: If you're finding black spots on the stems of your hydrangea, it could be perfectly normal, especially if all the stems have the spots. The black spots are lenticels and they are part of the vascular system of your plant. They have kind of a corky look to them. They are nothing to worry about. 

There might be a concern if your plant also has black spots on the leaves. Leaf spots are caused by fungi or bacteria. Brown or black spots and patches may be either ragged or circular, with a water soaked or yellow-edged appearance. Insects, rain, dirty garden tools, or even people can help its spread. To prevent and control: Remove infected leaves when the plant is dry. Leaves that collect around the base of the plant should be raked up and disposed of. Avoid overhead irrigation if possible; water should be directed at soil level. For fungal leaf spots, use a fungicide according to label directions.

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