Between 40 to 50 degrees.
Temperature Thresholds. According to Protabase, geraniums grow well in the temperature range of 65 to 95 degrees F during the growing season, and in the winter low temperatures between 40 to 50 degrees F, according to the A-Z Encyclopedia of Garden Plants.. 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. The temperature to propagate geraniums is ideally above 60 degrees F. Take cuttings 3 to 4 inches in length from the growing tips of branches in September to October. This allows three to four weeks for roots to develop before the first frost. Geraniums root easily from cuttings. Geraniums growing in pots are brought indoors in areas where the temperature drops below freezing. Geraniums in the flowering genus Pelargonium are tender perennials, meaning they can be grown as perennials in areas where the temperatures do not drop below freezing and as annuals in colder climates. If you live in U.S. Department of Agriculture plant hardiness zone 10b, you can grow them outdoors all year round. Temperature Range for Geraniums. Cultivars of the geranium species typically available at garden centers and nurseries grow best in daytime temperatures between 65 to 75 F and nighttime temperatures between 50 to 60 degrees F. Overview. Geraniums prefer temperatures over 60 degrees F. Temperatures below this cause leaves to turn rosy red and become weakened. Growth slows, but plants generally do not die. Geraniums perform best with 6 hours of sunlight per day. 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.
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what is the lowest temp for geraniums