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Minimum Temperatures for Geranium Plants

Updated July 19, 2017

The garden geranium is favoured because of its easy care and brightly coloured blooms. However, plants of the genus Pelargonium do not thrive if kept in extreme temperatures. Although they may survive a light frost, geraniums are not cold hardy.

Indoors

Although geraniums survive at a range of temperatures, for best growth and flower production, plants potted indoors are kept at a minimum daytime temperature of 18.3 degrees Celsius and placed by a window receiving maximum sunlight, ideally 10 to 12 hours per day. At night, geraniums produce best at a minimum temperature of 12.8C; at lower than 10C, leaves turn reddish and growth almost stops.

Outdoors

Because geraniums will not survive prolonged exposure to subfreezing temperatures, do not plant outdoors until safely past your last-frost date and when ground temperature has reached a minimum of 15.6C. For rapid production, geraniums prefer a minimum daytime temperature of 21.1C and a minimum night temperature of 15.6C. Remember, however, that at daytime temperatures of 26.7C or higher, geranium production will decline significantly.

Special Conditions

Note that minimum temperature variation may exist among some species, such as Martha or Lady Washington geraniums (Pelargonium domesticum). Additionally, geraniums overwintered using dormant storage should be kept at 7.22 to 10.0C.

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About the Author

Rachel Delp has been writing and editing for academic and medical publications since 1992. She is based in the mountains of southern Spain and her work focuses on health care, travel and culinary subjects. Her articles can be found on various websites. Delp holds a Bachelor of Arts in Spanish with a minor in art from Moravian College.