Frequently Asked Questions about Evapotranspiration (ET) Irrigation Controllers


Evapotranspiration is the amount of water that is released into the atmosphere through evaporation and plant transpiration. An evapotranspiration irrigation controller is a device that uses data about the landscape, the type of irrigation system, and local weather conditions to determine when and how much to irrigate. This 5-page fact sheet written by Paul Monaghan, Ondine Wells, Michael Dukes, Maria Morera, and Laura Warner and published by the Department of Agricultural Education and Communications explains how the technology functions as well as how to install, program, operate, and maintain an ET controller for a money- and water-wise sustainable home landscape that’s lush and beautiful.

Measuring the Irrigation Requirement of Container-Grown Nursery Plants (ENH1197/EP458)

Figure 3. Irrigation collection cups are placed above canopy in the vicinity of test plants.Three factors determine the irrigation requirement for container-grown crops: evapotranspiration, capture factor, and distribution uniformity. This 4-page fact sheet describes how these factors can be measured so that irrigation requirements can be determined in the container nursery. Written by Jeff Million and Tom Yeager, and published by the UF Department of Environmental Horticulture, June 2012.

Net Irrigation Requirements for Florida Turfgrass Lawns, Part 2: Reference Evapotranspiration Calculation (AE481)

Diagram of evapotranspirationUrban water users need specific recommendations to irrigate efficiently and for planning and regulatory programs. As the second step in the process of estimating net irrigation requirements, This 9-page fact sheet calculates reference ET for ten locations in Florida and one in Alabama. Written by Consuelo C. Romero and Michael D. Dukes, and published by the UF Department of Agricultural and Biological Engineering, August 2011. (Image from

AE459 Step by Step Calculation of the Penman-Monteith Evapotranspiration (FAO-56 Method)

AE459, a 12-page fact sheet by Lincoln Zotarelli, Michael D. Dukes, Consuelo C. Romero, Kati W. Migliaccio, and Kelly T. Morgan, provides a step-by-step calculation of the reference evapotranspiration (FAO-56 method) for a given location from the available weather data. Includes references. Published by the UF Department of Agricultural and Biological Engineering, February 2010.

AE445 Smart Irrigation Controllers: Programming Guidelines for Evapotranspiration-Based Irrigation Controllers

AE445, a 6-page illustrated fact sheet by Michael D. Dukes, Mary L. Shedd, and Stacia L. Davis, is part of the Smart Irrigation Controllers series. It presents programming guidelines for several examples of ET controllers available in Florida. Includes references. Published by the UF Department of Agricultural and Biological Engineering, February 2009.