Common geraniums, known botanically as Pelargonium sp., are common summer annuals prized for their clusters of blooms and their velvety green, trailing foliage. According to the University of Massachusetts at Amherst, the effect of temperature on geranium growth and performance is substantial, but varies by species — of which there are more than 14 — according to the U.S. Department of Agriculture. Treating geraniums as tender warm-season plants and observing general temperature guidelines will ensure peak rate of growth and flowering capacity.
In addition to cold temperature sensitivities, geraniums do not perform well under excess heat either. Choose a growing location where ambient daily temperatures stay at 80 degrees or below to prevent performance-impacting heat stress and leaf burn.