Elevated soil temperature is detrimental for potato tuber yield, starch content and processing quality. The effects of cool soil temperature are less well understood. In a series of experiments, seed potatoes of several chip and fresh market varieties were planted in greenhouses having a 16-h photoperiod and day/night air temperature of 22/18 ËšC. Shortly after emergence, some pots were transferred to insulated boxes that contained cooling coils that wrapped around individual pots. With this system, soil temperature was approximately 9-13 ËšC in the cooled pots and 17-21 ËšC in the control pots. The aboveground shoot was not chilled. Tuber number increased consistently and substantially for plants grown with the cooled soil treatment. Total yield, however, was comparable between the two treatments. When stored at 13 ËšC, potatoes from the chilled soil treatment sprouted sooner than those from the ambient treatment, with larger tubers sprouting earlier than smaller tubers. Skin color of Red Norland was much less red with the cooled soil treatment, whereas skin color of Adirondack Blue was darker purple with the cooled soil treatment. These data clearly indicate that soil temperature influences tuber set and size profile. They also demonstrate that tuber temperature influences the biochemistry underlying accumulation of anthocyanin pigments in the potato skin.