Technical Abstract: Water availability for turfgrass systems is often limited, and likely to become more so in the future. These experiments examined the ability of tall fescue (Festuca arundinacea Schreb.) to control transpiration with increasing vapor pressure deficit and whether control was influenced by temperature. The first studies were in steady-state conditions at two temperatures (21°C and 27°C) and two vapor pressure deficits (1.2 and 1.8 kPa). At the lower temperature, water use was similar at both VPDs, indicating a restriction of transpiration at high VPD. At 27°C, transpiration control at high VPD was weakened, and root growth also declined; both responses increase susceptibility to water-deficit stress. Another series of experiments examined the physiological stability of the transpiration control. Temperature and VPD were adjusted in a stepwise manner and transpiration measured across a range of VPD in the days following environmental shifts. The results indicated that VPD control acclimated to the growth environment, with adjustment to drier conditions becoming evident after about 1 week. Control was again more effective at cool than at hot temperatures. The results, collectively, indicate that transpiration control by this cool season grass is most effective in the temperature range where it is best adapted.