Monitoring leaf temperatures and environmental dynamics in propagation greenhouses

• Infrared radiometer temperatures were within ±0.5 °C of thermocouple measurements. • A thermistor exposed to sunlight over-estimated leaf temperature by up to 11.2 °C. • Leaf temperature dropped within 2 min after each mist irrigation event. • Average leaf and air temperatures varied by up to 3.2 °C in commercial operations. Accurate measurement of leaf temperature in plant cuttings is needed to schedule mist irrigation based on leaf vapor pressure deficit, and in order to maintain optimal temperature ranges for photosynthesis and root development. Commercial propagation greenhouses frequently employ “Artificial Leaf” thermistors exposed to light to represent leaf temperature, but sensor performance under mist irrigation is poorly documented. This study evaluated two non-contact infrared (IR) radiometers (Apogee SI/SIF-111-ss and Omega OS151-LT/OS211-LT) against contact thermocouples, fine-wire thermistors, and an Artificial Leaf, and examined environmental determinants of the leaf minus air temperature difference (LAD). 1-min measurements of leaf temperature and climate data were collected over seven days in a university greenhouse with Chrysanthemum × grandiflorum cuttings and analyzed using SAS. Complementary IR datasets were collected from seven commercial propagation greenhouses across the United States. All sensors had similar measurement during the night period. However, during daylight the Artificial Leaf over-estimated thermocouple temperature by 2.2 to 11.2 °C and exhibited high variability compared with thermocouples. Both IR radiometers resulted in similar values to thermocouples during daylight hours. In commercial greenhouses average LAD ranged from −1.6 to +3.2 °C and was most positive in greenhouses using high-pressure sodium lighting. Misting events reduced LAD within seconds, indicating rapid evaporative cooling. This study highlights that the industry-standard Artificial Leaf temperature sensors are highly inaccurate with up to 11.2 °C error, whereas IR radiometers deliver accurate, non-contact leaf temperature monitoring under propagation conditions which would improve the ability to dynamically control mist frequency, thereby improving water-use efficiency and cutting quality. CONTEXT: Leaf temperature strongly influences water status, stress responses, and rooting success in unrooted cuttings. Commercial propagation greenhouses commonly employ “Artificial Leaf” thermistors positioned above mist emitters for mist irrigation scheduling, but these sensors may not accurately reflect leaf cooling under misting. Contact sensors such as thermocouples provide accurate readings but are impractical in commercial operations due to labor and handling challenges. Non-contact infrared (IR) radiometers offer a potential alternative, but their performance under propagation conditions has not been validated. OBJECTIVE: This study evaluated the accuracy of different leaf temperature measurement methods for unrooted cuttings, with a particular focus on validating IR radiometers and Artificial Leaf thermistors against thermocouples. A second objective was to characterize environmental factors affecting leaf–air temperature differences (LAD) in both research and commercial propagation greenhouses. METHODS: Comparisons of sensor performance were conducted in a University of Florida greenhouse with Chrysanthemum × grandiflorum cuttings. Five sensor types were tested: thermocouples, fine-wire thermistors, IR radiometers (from Apogee and Omega), and an Artificial Leaf thermistor. Data were logged at 1-min intervals over seven days and analyzed with linear mixed models – a statistical approach for repeated measurements that accounts for both random and fixed effects. Complementary trials in seven U.S. commercial propagation greenhouses, spanning the Eastern United States, deployed IR radiometers to monitor leaf temperature in relation to air temperature, relative humidity, radiation, and mist scheduling methods. Collection of data from multiple climatic regions helped to verify that IR radiometers would provide reliable, generalizable leaf-temperature monitoring across a range of propagation environments. RESULTS AND CONCLUSIONS: In the research greenhouse, all sensors agreed during nighttime, but the Artificial Leaf thermistor overestimated daytime leaf temperature by 2.2–11.2 °C compared with thermocouples. Both IR radiometers closely tracked thermocouple measurements across diurnal cycles, with lower residual variance than the Artificial Leaf. Leaf temperature dropped immediately following mist events, confirming rapid evaporative cooling. Commercial greenhouse data showed LAD values ranging from -1.6 to +3.2 °C, with the most positive LAD observed in facilities using high-pressure sodium (HPS) lighting. These findings demonstrate that IR radiometers provide accurate, non-invasive monitoring of leaf temperature under propagation conditions, whereas Artificial Leaf thermistors substantially overestimate leaf heating. SIGNIFICANCE: Accurate, real-time monitoring of leaf temperature is critical for optimizing mist irrigation, water-use efficiency, and cutting quality in propagation systems. This study supports the replacement of Artificial Leaf thermistors with IR radiometers in commercial propagation greenhouses characterized by high humidity and frequent mist irrigation. Adoption of non-contact IR sensing enables dynamic mist control based on actual leaf conditions, reducing water waste and mitigating stress in unrooted cuttings.