It is important that the soil drains well and that water doesn't stand around them. Infrequent deep watering of bedded geraniums is better than frequent light sprinkles. Water potted geraniums only when the soil is dry. Anything less than full sun will result in a poor specimen. Indoors, keep them as close to a southern window as possible.
Black leg is prevalent.
It is fostered by high humidity and wet soils. Never propagate plants from infected plants. Destroy any plants that are infected. Good cultural practices, including the removal of dead flowers and leaves from the plant as well as from the soil around the plants should be done diligently. Never water the plants in late afternoon or evening, and avoid watering the leaves and flowers.