Smart Irrigation Month

By Dan Sandor

irrigation month logo

July is annually recognized by the Irrigation Association as Smart Irrigation Month, but what does it mean to utilize smart irrigation? In a time of smartphones, smart watches, smart appliances, and smart homes why shouldn’t your lawn’s sprinkler system be just as intelligent? Over the last decade, new improved technologies, such as soil moisture sensors and smart irrigation controllers have entered the residential and commercial market and can be used to upgrade your current sprinkler system.

In the Land of 10,000 Lakes, water is seemingly plentiful, but an abundance is still no excuse for negligent water use, whether it’s indoor or outdoor. Of course it’s much easier to identify sources of indoor water waste, such as leaving the faucet running while brushing your teeth or washing half loads of laundry or dishes. However homeowners and property managers may be unaware of how much water is applied, and therein wasted, through their programmed irrigation schedules; it is very likely more water is being applied than is actual necessary.

It is important to bear in mind that irrigation should be only utilized as a supplement to rainfall, and not used as the primary source of water for the lawn. Here in the Twin Cities we received a combined 9.4 inches of rain during May and June this spring (Figure 1), which was approximately 25% more rain than our 30-year average during these months; so the likelihood of even needing to even irrigate so far this spring / early summer has been very minimal. The national weather service provides historical, 30-year temperature and rainfall data for most cities in each state and you can compare the 2019 year-to-date precipitation against the 30-year data for your area.

Bar chart with historical and 2019 rainfall data for May through June in inches.
Figure 1. 30-year average rainfall data during May + June rainfall compared against 2019 observed data for May + June (*complete 2019 May + June rainfall data were unavailable for NW Minnesota cities). National Centers for Environmental Information, 2019.

So now that we have transitioned from a wet spring into summer’s heat, how can you make smart choices and participate in smart irrigation month by watering more wisely? To begin with, the most efficient way to irrigate your lawn is to simply leave the controller in the OFF position and only irrigate when absolutely necessary (when the turf begins to show some drought stress). You may consider lowering your expectations as well; a little brown isn’t necessarily bad and the turf will recover upon significant rainfall or after the next scheduled irrigation event (Figure 2).

Non-irrigated plot with brown turf before receiving precipitation; after precipitation, the non-irrigated plots are mostly green
Figure 2. Top: A non-irrigated Kentucky bluegrass lawn in St. Paul, MN that had not received any rain for over two weeks during the heat of the summer. Bottom: The same lawn after receiving 2.2 inches of rain during the two-week interval. In the area immediately above the blue-dashed line in the top photo you can see irrigated plots of the Kentucky bluegrass, however in the bottom photo it is more difficult to discern the irrigated from non-irrigated plot.

The state of Minnesota requires all automated irrigation systems installed after July 1, 2003 to have technologies installed, such as a rain sensor, soil moisture sensor, or smart controller, to prevent or stop unnecessary irrigation during periods of sufficient moisture. Some advantages and disadvantages of these three technologies are listed in Table 1 below.

Table 1. Advantages and disadvantages of rain sensors, smart controllers, and soil moisture sensors.
Technology Advantages Disadvantages

Rain Sensors

  • Easily affordable ($20-30)
  • Many are available as wireless models
  • Relatively easy to install
  • Cork discs can become less sensitive to rain over time as discs age and are continually exposed to elements (short life span, ~1 to 3 years)
  • Sometimes installed incorrectly (indoors, under tree branches, roof overhangs and / or gutters), inhibiting their maximum water-savings potential
  • Water savings are minimal compared to smart controllers and/or soil moisture sensors

Smart Controllers

  • Uses real-time, local, environmental conditions to adjust scheduled run-times
  • Some of the newest models work with smart technology like Amazon Alexa and Google Home
  • Able to isolate specific zones from the smart irrigation adjustments
  • Use either auto-adjustment or user-adjusted settings to further reduce water use
  • Purchasing costs can be high (>$150-200) depending on the number of zones
  • Most require a smartphone to adjust and / or maximize program settings
  • Requires strong, continual access to Wi-Fi to make water-savings adjustments

Soil Moisture Sensors

  • Provides an accurate estimate of how much water is available in the soil rootzone where water is actually absorbed by the turf
  • Calibrated soil moisture threshold can be adjusted to fit the user’s preference
  • Some models provide the capability to isolate other zones from the soil moisture sensor
  • Some are available as wireless models, but most models require a small amount of digging and trenching of wire back to the existing in-ground valves
  • Installation and calibration procedures must be followed closely to maximize water-savings potential of the sensor
  • User must remember where sensor is installed when performing other lawn care practices like aerification

Rain sensors and soil moisture sensors bypass scheduled irrigation programs completely due to either significant rainfall or sufficient soil moisture – essentially turning off the controller (Figure 3). Smart controllers utilize historical, or current, regional weather data to make adjustments for the scheduled irrigation program. Most smart controllers utilize Wi-Fi to communicate with local weather stations to adjust program runtimes, while others may come with a weather sensor to utilize on-site weather data for making runtime adjustments. Your property may have multiple irrigated zones including areas like gardens, trees, shrubs, and ornamental & bedding plants that may require more frequent watering than turfgrasses. Upgrading your sprinkler timer to a smart irrigation controller or installing a soil-moisture sensor in the lawn, are two ways to isolate the yard from these other irrigated zones. The Irrigation Association and the EPA Water Sense program have resources to help you locate and learn more about these specific technologies.

Soil moisture sensor user-interface add-ons
Figure 3. Soil moisture sensor user-interface add-ons which connect to the existing irrigation timer providing communication between the in-ground sensor and the timer. In these photos, the dial for in timer is in the RUN position; however the sprinkler system will not run because, as indicated in the yellow circles, watering has been suspended (left) or the timer is been turned off (right) due to sufficient soil moistue in the turfgrass rootzone. Additionally, each of these user interfaces allow the calibrated soil-moisture threshold to be adjusted (+/-) by the user.

Finally, one of the smartest irrigation practices to follow is to conduct an irrigation audit, whichyou should do this regardless of whether you have a traditional or smart irrigation system. We generally recommend this is conducted once every year, usually in the spring. As most irrigation programs run late overnight or during the early hours of the morning, it is likely unknown if the sprinkler system is even running properly and / or if water is being applied in an efficient manner. The first step in an irrigation audit is to run a manual cycle for each zone in your system, then you will be able to make sure all the heads are aligned correctly to prevent unnecessary watering of impervious surfaces and other non-target areas. During the manual cycle also check for any broken heads / nozzles and for leaks that may be coming from underground around fittings, valves, and joints. Once all the heads are aligned and all leaks have be repaired, you can begin the catch-cup test; information on how to perform that test is provided here by UMN Extension. Once you have completed the test you can program the runtimes and then let the rain sensor, soil moisture sensor, or smart irrigation controller take it from there.

July isn’t the only month of the year to practice smart irrigation. In fact, you should start every spring by auditing your sprinkler system and evaluating each zone for any leaks and repairs that will need to be made before you begin programming zones for the summertime heat. After you finish the auditing procedure you may be just fine keeping your system turned off, for your lawn at least, and turning it on only when you need to. If that’s not an option, then consider investing in a soil moisture sensor or upgrading to a smart controller and become a more intelligent irrigator and finer steward of a precious resource.

Further Reading:

Cardenas-Lailhacar, B. and M.D. Dukes. 2008. Expanding disk rain sensor performance and potential irrigation water savings. J. Irrig. Drain. Eng. 134:67-73.

Cardenas-Lailhacar, B. and M.D. Dukes. 2012. Soil moisture sensor landscape irrigation controllers: A review of multi-study results and future implications. Trans. ASABE. 55:581-590.

Carrow, R.N. 2006. Can we maintain turf to customers’ satisfaction with less water? Agric. Water Manag. 80: 117-131.

Dukes, M.D. and D.Z. Haman. 2017. Residential irrigation system rainfall shutoff devices, or rain sensors. UF/IFAS Extension. Bul. ABE325.

Dukes, M.D., M. Shedd, and B. Cardenas-Lailhacar. 2015. Smart irrigation controllers: How do soil moisture senor (sms) irrigation controllers work? UF/IFAS Extension. Bul. AE347.

Fender, D.H. 2008. Urban turfgrasses in times of a water crisis: benefits and concerns. In: J.B. Beard and M.P. Kenna, eds., Water quality and quantity issues for turfgrasses in urban landscapes. Council for Agricultural Science and Technology, Ames, IA. p. 11-31.

Grabow, G.L., I.E. Ghali, R.L. Huffman, G.L. Miller, D. Bowman, and A. Vasanth. 2013. Water application efficiency and adequacy of ET-based and soil moisture-based irrigation controllers for turfgrass irrigation. J. Irrig. Drain. Eng. 139:113-123.

Leinauer, B. and D.A. Devitt. 2013. Irrigation science and technology. In: J.C. Stier, B.P. Horgan, and S.A. Bonos, editors, Agronomy Monograph 56 Turfgrass: Biology, Use, and Management. American Society of Agronomy, Crop Science Society of America, Soil Science Society of America: Madison, WI. p. 1075-1131.

Leinauer, B. and R. Green. 2011. Water management technologies. In S.T. Cockerham and B. Leinauer, eds., 2011. Turfgrass water conservation. University of California Agriculture and Natural Resources. 2nd edition. Publication 3523:101-112

Meeks, L., M.D. Dukes, K.W. Migliaccio, and B. Cardenas-Lailhacar. 2012. Long term expanding-disk rain sensor accuracy. J. Irrig. Drain. Eng. 138:16-20.

Muñoz-Carpena, R. 2018. Field devices for measuring soil water content. UF/IFAS Extension. Bul. BUL343.