The effects of short exposures to low temperature on cotton (Gossypium hirsutum L. ‘Stoneville 213′), velvetleaf (Abutilon theophrasti Medic), and spurred anoda [Anoda cristata (L.) Schlecht.] were studied in controlled environment chambers. A 3-day exposure to 17/13 C day/night temperatures 24 days after planting significantly reduced dry weight, leaf area and height in all three species when compared to control plants maintained at 26/21 C day/night. After subsequent periods of 7 days at 26/21 C and 8 days at 29/23 C, the two weed species recovered in growth more completely than did cotton. Therefore, the weed/crop ratios for dry weight and leaf area were increased by the imposition of the cold treatment. Mathematical analysis of the growth of the three species indicated that the growth reductions during the cold treatment were caused by decreases in both net assimilation rate and leaf area duration. The net photosynthetic rates and stomatal conductances of individual leaves of cotton and velvetleaf were significantly reduced during the cold treatment but recovered to control levels during a subsequent 4-day exposure to 26/21 C. We conclude that the adverse effects of low temperatures on the growth of cotton, velvetleaf, and spurred anoda are caused mainly by reductions in leaf area production. Because of its slower and less complete recovery, cotton is more severely affected by low temperature than either of the two weeds. Our results help explain the observation that velvetleaf and spurred anoda are more competitive with cotton following abnormally cool periods early in the growing season.