Geraniums can be grown indoors as houseplants year round, and if desired, you can take them outdoors to a patio or another sunny area during warm weather. Alternatively, you can transplant geraniums into your garden, but note that even though geraniums are perennials plants, in cooler climates, they are often grown as annuals. If you have geraniums waiting to go outside, be sure you wait until the right time so they have the best chance to establish themselves and then grow and bloom well.
Do not move your geraniums outdoors until the danger of frost is passed. When this exactly happens varies from climate to climate, but can occur anytime from March, such as in parts of Florida, until July, such as in parts of Colorado. If you have potted geraniums and you take them out early, move them indoors or to a garage on nights when frost is expected.
If you’re planning on transplanting your geraniums outdoors into your garden, soil temperatures should be at least 60 degrees F. Use a soil thermometer to measure the soil’s temperature. Be sure to choose a location in the sun, since geraniums need lots of sunlight to thrive.
To help geraniums acclimate to outdoor conditions, place them outside near their final location for a couple hours and then, everyday, increase how much time they are placed outdoors by a couple more hours. Start this process a week before you plan to move them outdoors permanently. On the last day, they are ready to "spend the night" outside (as long as frost is not a concern). Your geraniums will now suffer less stress during the transition process from indoors to out than if they had be brought outdoors all at once.
Bring your potted geraniums back indoors in the fall when frost is once again an issue. Acclimate them to the indoors like you did the outdoors. You can grow them as houseplants in a sunny area of your home. Don’t forget to keep the soil slightly moist and keep plants away from heat sources and drafts. Note that garden geraniums will die back like annuals if they are not hardy in your climate. Most geraniums are hardy in U.S. Department of Agriculture zones 8 and warmer.