Retrofitting done right

Features - Irrigation

Making an old system new can be a challenge. Follow these tips to make the process smoother.


The availability of smart irrigation technologies for improving landscape irrigation, such as soil moisture sensors (SMS) and evapotranspiration-based (ET) controllers, has excited many.

We can use these tools to improve landscapes by applying the right amount of water for our plants while also lowering our water bills.

For a new home and a new irrigation system, this can be done fairly easily. However, we are often faced with taking an older system and “retrofitting” or modifying it to use the smart irrigation technology.

In fact, this can be quite the headache if the irrigation system uses an indexing valve, which is a special type of valve that is sometimes used in place of electric valves.

Water enters the valve and is distributed to one of the out-going lines or zones, irrigation stops and water pressure drops, the valve switches to the next out-going line or zone, and so-on depending on how the timer is set and how many lines are used. If the goal is to use SMS-based or ET controller irrigation technologies, indexing valves are not the most desired pairing.

The SMS and ET smart technologies were intended to be used with electronic valves as these provide the flexibility needed to more efficiently apply irrigation to the landscape with variability among zones.

For a SMS-based system, soil moisture sensors are placed in the landscape to measure water content in the root zone of the irrigated plants. Irrigation occurs or does not occur based on this measurement and timer settings.

Obviously, different types of landscape plants (hopefully separated by zones) will have different plant water uptake and water evaporation (aka ET) and thus not require the same amount of irrigation.

The ET-based system applies irrigation based on this concept, thereby only applying water as needed. ET controllers typically use information provided by the user about the particular area being irrigated and weather data to estimate irrigation needs.

Users enter information by zone so that differences among zones are considered in determining run times. The concept of irrigating zones differently requires electronic valves as indexing valves were not designed for such application.

A complication that can arise from modifying a system from an indexing valve to electric valves is that many irrigation systems with indexing valves also have mechanical timers. To use the smart irrigation technology, a digital timer is needed.

The use of on-site irrigation wells for landscapes is common in Florida so it is not unusual to see an irrigation well, a mechanical timer and an indexing valve as the irrigation framework.

Retrofitting this type of system to smart irrigation requires switching to a digital timer, some additional electrical work to trigger the well pump (a pump start relay) and replacing the indexing valve with electrical valves.

While this is an investment, the end result will be a beautiful landscape with more efficient irrigation and, where potable water is concerned, lower water bills.

Migliaccio and Gutierrez work for the University of Florida. McCready was an extension agent in Miami-Dade County.