This experiment was undertaken to investigate the effect of root zone temperature during the night on absorption of mineral nutrients, growth, and fruit yield of the truss-limited hydroponic tomatoes in winter. The root zone temperature was either controlled to 10, 15, 20, $25^{circ}C$, or left uncontrolled at ambient temperatures. Temperature of the covered beds rose as root zone temperature was raised, but it in all treatments was less than 3$^{circ}C$ higher than that in the control. Raising root zone temperature, except $25^{circ}C$, showed positive effect on plant height, leaf length, stem diameter, and plant fresh and dry weight, but not on T/R ratio which was the greatest in the control. Root activity in all treatments except $25^{circ}C$ increased as compared to the control. Mean fruit weight, fruit count per plant, and fruit yield were the greatest in 2$0^{circ}C$ treatment. Root zone temperature did not significantly affect the contents of total nitrate and magnesium in leaves, stems and roots. Concentrations of phosphate and calcium increased in leaves and stems, but decreased in roots as root zone temperature increased. Overall, 2$0^{circ}C$ treatment gave the greatest growth and energy efficiency.