Wood chips, pine bark and composted yard waste can be used as mulches. Occasionally cutworms or caterpillars will feed on geraniums. They can be readily detected by the cut edges of the leaves where they feed. If only a few are responsible for damage, they should be destroyed individually rather than spraying the entire bed. The most common diseases that attack geraniums are non-specific in that they attack other plants as well.
Plants infected with blackleg disease have a shiny, coal-black, slimy appearance.
The rot progresses rapidly, often killing plants within a week. A commercial fungicide specific for Pythium can be used if the disease is in the initial stages. Botrytis, caused by the common gray mold Botrytis cineris, produces spores which are airborne and germinate when they come in contact with wet foliage and flowers. To control Botrytis blight, avoid watering foliage and flowers, especially in the late evening and when the humidity is high. Also, since Botrytis starts most frequently on old decayed leaves and flowers, remove and destroy them.