Over 200 species of geraniums exist, according to the University of Minnesota. Geraniums are hardy indoor-outdoor plants, but you must consider several factors as you plan to move them outdoors.
Move the geraniums outdoors after the last spring frost. The soil temperature should be around 15.6 degrees Celsius. The warmth will also make the soil more porous, providing the drainage that geranium requires.
When you plant the geranium plants outside, place them in a location where they will receive at least eight hours of sunlight per day. Less light makes the geranium bloom less profusely. Use mulch or perlite to help the geranium retain its water.
Heat from the spring and summer sun makes the geranium more prone to drying out. Water the plant frequently, especially if you are placing them in plastic containers; the plastic creates a greenhouse effect and dries out the soil faster.