Chrysanthemum plants were exposed to 16°C day-temperature, 11°C night-temperature, 13°C soil-temperature, to be indicated as 16/11/13°C, or to 16/11/25°C, 20/16/18°C, or 20/16/25°C, first long day, then short day, (long day = 12-h light period with 3-h night break; short day = 12-h light period) from planting to harvest in controlled environments to study the effects of soil heating on growth and flowering. There were significant, but not substantial, effects of soil heating on leaf area, percent soluble carbohydrate, flower bud diameter, days to visible bud and some other parameters. Two winter cultivars responded similarly, while 2 summer cultivars differed in flowering-response to soil heating. An experiment was also conducted using 16/11/25°C day/night/soil temperatures during long days, short days or throughout the complete growth cycle, with 16/11/13°C day/night/soil temperatures at other times. Soil heating during long days resulted in the highest quality flowers. Soil heating during short days or throughout the growth period resulted in most rapid flowering but decreased flower quality.