Methods for the precise control of drought stress have been a holy grail of plant biology research.  Here we describe a five-container growth chamber system and a 16-container greenhouse system, each of which uses load cells to precisely monitor and control the mass of a soil/plant system.  The calibration and signal conditioning necessary to quantify transpiration over 10 minute intervals is described. Evaporation can be reduced to less than 1% of the transpiration rate by covering the container surface. Procedures for quantifying and correcting the effect of temperature on load cell output are described. Each system can be programmed to maintain a steady-state reduction in transpiration compared to well-watered control plants, and can continuously monitor whole-plant stomatal conductance. Mini-lysimeters are also useful for quantifying physiological water use efficiency, whole-plant stomatal oscillations, and plant-available water in the root-zone. Example data for each of these parameters is provided.