Geraniums require moist, well-drained soil, rich in organic matter. They are heavy feeders and need regular fertilization. They need to be watered in the absence of rainfall. Full sun -- 6 to 8 hours a day -- will help them grow their best.
Geraniums photosynthesize sunlight into plant sugars for energy. Because they are fast growers and prolific bloomers, they use a lot of energy. The slightly pubescent texture of geranium leaves also necessitates prolonged sun exposure.
If planted indoors, geraniums should be given as much sunlight as possible. A sunny window is best. Grow lights can supplement light, if needed. On a porch or shady patio, choose the brightest spot.