For optimal growth and flower production, geraniums require eight or more hours of sunlight per day. A sun-hungry plant, the geranium thrives on as much sunlight as it can receive. Plants subjected to inadequate light will produce few blossoms.
Overwinter geraniums in containers indoors. Place the container indoors in a window with bright direct sunlight. A south-facing window is ideal if the plant receives at least eight hours of sunlight per day. Keep the plant moist but not overly wet. Geraniums successfully overwintered indoors can be planted back outdoors in a sunny location after all danger of frost has passed.
If geraniums cannot have adequate sunlight indoors during the winter months consider using supplemental fluorescent tube lighting. Suspend the lights 10 to 12 inches above the plant. Turning the lights on during the winter months from 6 to 10 p.m. will help provide adequate light for the plants. Turn the lights off during the night to allow the plant’s biological clock to cycle naturally between night and day.
The foliage and flowers of the geranium plant enjoy full sunlight but the plant’s root system prefers to remain cool and moist. Consider applying 2 to 3 inches of mulch around the base of the plant. The geranium grows best when the daytime temperature hovers at 65 degrees Fahrenheit and the nighttime temperature dips to 55 degrees Fahrenheit.