More than 10,000 geranium (Pelargonium spp) cultivars, both bushy and trailing, exist. When these normally tough and drought-tolerant performers begin wilting, something is amiss.
Two major causes of wilting geraniums are bacterial blight from an infestation of Xanthomonas campestris pv. pelargonii germs, and root rot from Pythium or Rhizoctonia fungi.
Root rot-infested plants have brown or black spots encircling their bases. In humid conditions, diseased geraniums may develop whitish to gray webs. Severe infestations cause decaying roots and yellow, wilting branches and leaves.
Blight-infected geraniums have wet or brown spots on their lower leaf surfaces. Their leaf veins may darken, and their leaf margins wilt. Branch wilt and black, rotting stems indicate systemic infection. Infected ivy geranium are exceptions. Instead of wilting, they develop symptoms similar to those of insect infestation or nutritional deficiency.
Replace infected plants with healthy ones. Amend the soil if necessary to improve drainage and eliminate standing water. Limit nitrogen-based fertilizer applications. Apply fungicide directly to the soil.
Replace infected plants with healthy ones spaced for adequate air circulation. Water the plants from beneath early in the morning. Amend the soil if necessary to improve drainage.