With appropriate care and enough sunlight, geraniums grow well indoors, according to the University of Minnesota Extension. Fluorescent lights 10 to 12 inches from the plants can supplement natural light and help indoor geraniums thrive.
Touch the geranium’s soil before watering. If it feels dry, water thoroughly, but if it feels moist, don’t water; excessive watering makes geraniums rot.
Indoor geraniums that are potted in a good soil mix (one part soil, one part sand, one part peat, according to the University of Minnesota Extension) will not require additional fertilization for two to three months. Geraniums that are kept indoors year-round should be fertilized only during growth periods.
The ideal temperature for geraniums is 65 degrees during the day and 55 degrees at night. Geraniums grown indoors should not be placed in cold, drafty spots, such as near a poorly insulated window, or in hot, dry places, such as near a radiator.
Geraniums grown indoors should be pruned or pinched regularly.
If geraniums are being grown indoors from seed, they may be started in mid-January. They should be kept at 75 degrees during germination. Until being transplanted outdoors, these seedlings should receive 16 to 20 hours per day of fluorescent lighting 3" to 4" away.