|Geranium plants can be overwintered in several ways. Before frost, whole plants can be taken from the garden, tied in bundles, and hung upside down in a cool moist area such as a basement for the winter. The humidity should be at least 80% and the temperature should be between 35 and 45° F. The plants can be cut back to about 1/3 of their height and planted outdoors in May, or potted indoors in late winter.
You can also dig the plants and overwinter them indoors in a sunny window. Take as much of the root system as possible. Place the plant in a pot large enough to accommodate the root system, cut the plant back to 6 inches in height. Geraniums also can be overwintered from cuttings taken in late summer or early fall.