ABSTRACT Containerized plant growth is common in controlled environment research and the greenhouse industry.  Because of the small root-zones of containers, water availability changes rapidly over short time intervals.  To overcome this, irrigation is often excessive causing leaching.  Environmental concerns has prompted studies on improved irrigation efficiency.  Tensiometers equipped with low tension (fast response) ceramic cups and pressure transducers were used to measure and control water in a peat:perlite mix.  Plants were watered with a dilute nutrient solution when the water potential of the media decreased to either –5 or –20 kPa.  Irrigation continued for ten seconds or until the water potential of the media was greater than the setpoint.  Other researchers have used this technique to control watering but have compared effects of watering setpoints through fresh and dry mass at the end of the study.  A better technique is to make real-time measurements of plant growth.  We measured whole plant transpiration rate, leaf temperature, and leaf expansion as indicators of water availability. Transpiration was measured using a whole-plant open gas-exchange chamber, leaf temperature with a infrared thermometer, and leaf expansion with a digital camera.  Controlling irrigation with a tensiometer minimized leaching without affecting plant growth.