The popular garden geranium is not considered cold hardy, although plants may survive a light frost. If removed from the ground and preserved over winter, you may keep geraniums for more than one year. More robust hardy geraniums, however, are cold hardy.
Garden Geranium Hardiness
Garden geraniums, members of the genus pelargonium originating from South Africa, are hardy in U.S. Department of Agriculture zones 9 and 10. This means that these flowering plants can survive exposure to cold temperatures as low as -6.67 to -3.89 degrees Celsius. Therefore, in colder regions, garden geraniums are considered annuals.
Tips for Preserving
It is possible, however, to preserve your garden geraniums over winter even if you live in zone 8 or further north. You can dig out pelargonium species, repot and bring inside during cold months. Or you can dig up geraniums, remove soil from roots, wrap roots in newspaper and store in a cool, dry location until after the final frost.
Members of the geranium genus, also known as hardy geraniums or cranesbills, however, are considered cold hardy. These geraniums can survive temperatures as low as minus 20 degrees Fahrenheit or as far north as zone 5 in the United States. They will lie dormant during winter, growing new leaves in the spring.