Geraniums are popular plants grown both indoors and out. There are over 200 known species, most of which originated in South Africa. Although relatively easy to grow, geraniums do have specific soil preferences.
It is best to wait until the threat of frost has passed to plant geraniums outdoors, according to the University of Minnesota Extension, which recommends a soil temperature of at least 60 degrees Fahrenheit. Blooms will be more abundant with increased sunlight, so opting for an area with at least eight hours of sunlight per day is recommended.
The extension office, which warns against overfertilization, recommends mixing minimal amounts of fertilizer in the soil when preparing the area for planting. Two pounds of 10-10-10 fertilizer or four pounds of 5-10-5 dry fertilizer are generally recommended.
It is important to allow for irrigation during the summer months by digging furrows around the plants. Geraniums should be watered adequately but the soil should dry completely between waterings.
Planters can also be used outdoors to grow geraniums. Regular watering of plants in outdoor planters is necessary because of the increased temperature of the soil. Special care should be given to ensure that there are drainage holes in the bottoms of containers to promote regular drainage. Excess water collected in the bottom of planters can result in root rot.
Geraniums can thrive indoors if there is adequate light available. Fluorescent lights can be used as a substitute for natural sunlight if necessary. Watering should be based on the feel of the soil and is only necessary when the soil feels dry to the touch. As with outside planters, all containers must have holes to promote drainage.