Watering Times & Schedule

"Timing is Everything!"

Whether it is playing baseball, baking cookies, or jamming with the band, many things in life rely on proper timing – and watering your lawn is no different! Across our 35 years of experience with irrigation systems, one of the most common issues we have come across is people running their sprinkler zones for too long, or not long enough, or at the wrong time of day. 

Not knowing when and how long to run your sprinklers can lead to wasted water (and money), dry spots, and even issues with grass health! 

NOTE: if you’re looking for some starting points for proper sprinkler timing, you can jump ahead to our conclusion and samples:

We still recommend reading this to find the best ways of fine-tuning your watering times and schedule to make sure you aren’t wasting any unnecessary water!

To determine the perfect sprinkler system timing for each unique lawn, you will need to answer five important questions:

And if you would like some help programming the proper sprinkler watering times into your controller, check out our article on programming your controller [coming soon] and our videos for Rainbird and Hunter controllers below:

1) How green do you want your grass?

Most lawn grasses are selected because they look great and offer a comfy and durable area for recreation.  To maintain that lush, green appearance, lawns require a significant amount of water to keep them growing optimally, which often requires irrigation to supplement seasonal rainfall. 

This article focuses on how to set up your irrigation system timing to achieve this optimal watering without wasting excess water.  

However, if your goal is simply to keep your grass alive in-between rainfalls, you can reduce waterings according to those goals.  For example, well-established lawns consisting of Kentucky bluegrass can be left to go brown and dormant without water for up to 1 month and then bounce back beautifully when soil moisture is replenished1Beard, J. B. (1972). Turfgrass: Science and culture. Prentice Hall.

2) How much water does your lawn need?

Grass Type: 
Different types of grass need different amounts of water to grow (called “transpiration”). They take this water from the soil, which is then replenished through irrigation.

While bluegrasses can use over 10 mm of water per day, fescues and bermudagrasses typically use only 6 – 8 mm each day2Beard, J. B., & Beard, H. J. (2005). Beard’s Turfgrass encyclopedia for golf courses, grounds, lawns, sports fields. MSU Press. Therefore, a cool-season lawn mix consisting of Kentucky bluegrass and Tall fescue will reach its full potential with about 1.5 – 2 inches (38 – 50 mm) of water per week in a typical mid-latitude summer climate.  If your in a hot and dry climate with very low relative humidity, these water requirements can be up to twice as high3Carrow, R. N. (1995). Drought resistance aspects of Turfgrasses in the southeast: Evapotranspiration and crop coefficients. Crop Science35(6), 1685-1690, unless warm-season grass mixes with lower water needs are used to compensate.

However, depending on your goals, it is often possible to use even less water!  Although your lawn will not be at its maximum greenness, a healthy and great-looking lawn can typically be achieved using about 25% less water than your lawn might ideally prefer, resulting in significant water conservation.  In the case of the above-mentioned Kentucky bluegrass mix, you would be looking to provide 1 – 1.5 inches (25 – 38 mm) of water per week for your lawn.  This, however, comes down to your preference.

Technical Note
lysimeter is required to measure the actual amount of water used by your specific grass through both evaporation and transpiration (together called “evapotranspiration”) in a specific climate.  

Since lysimeters are expensive and time-consuming to implement, a good starting point is to check with the producer of your lawn’s seed mix for your lawn’s water needs.

Weather station estimates of evapotranspiration can also be helpful in factoring in regional climate, although they do not take into account grass/plant type.

This general weekly water requirement for your lawn can then be fine-tuned through the following two factors:

Sun Exposure: 
This one should make sense: grass areas that experience long periods of direct sunlight throughout the day will require more water than areas that are in the shade.  This is because the sun not only increases the evaporation of water from the soil (making less available to the grass), but also increases the water used by the grass to grow4Kim, K. S., & Beard, J. B. (1988). Comparative Turfgrass evapotranspiration rates and associated plant morphological characteristics. Crop Science28(2), 328-331.  

Therefore, you should run your sprinklers in shady areas for less time.  This is also why ideal sprinkler design allows sunny areas of the lawn to be watered separately from shaded areas. These different groupings of sprinkler heads that run together are called “zones“.

Weather fluctuations: 
If you live in an area that experiences seasonal temperature changes, your lawn will require more water during the hotter mid-summer periods of the season than in the cooler spring and autumn periods.  Daily weather fluctuations can also have an impact: windy and exceptionally hot conditions increase the amount of water needed due to increased evaporation, while overcast and unusually cool conditions decrease it.  

Adjusting your timing for these conditions can most easily be done through the “seasonal adjust” setting on your controller, as shown in our How to Program your Controller article (coming soon)!

Also, you can often save water by not irrigating right after it rains, as long as about 0.75 inches (19 mm) of rain fell within the day.  Adding a rain-sensor to your system can help take the guesswork out of this!

After considering your grass-type and environmental factors, you will now have a good estimate of your lawn’s weekly water needs in each sprinkler zone (but some trial-and-error might be needed)

Example: in a mid-latitude summer climate, a lawn of Kentucky bluegrass mix in a zone with mixed sun/shade will need about 1.2 inches of water per week to be green and healthy, while still conserving water.

3) How long should you run your sprinklers?

Now that you know how much water your lawn needs each week (see above section), you now need to match those water needs to the amount of water provided by your irrigation system. 

The amount of water your sprinklers put down over a given period of time is mainly controlled by the type of sprinklers and the overlap on your sprinkler coverage.  Together, these factors determine what is called the sprinkler system’s precipitation rate.

Technical Note
Heads that have a matched precipitation rate (MP or MPR)” means that their flow is adjusted so that water is put down at the same rate regardless of their spray arc (quarter circle vs full circle).  Otherwise, for sprinklers without a matched precipitation rate, the same head will put down more water over a quarter circle and less water over a full circle because the same water is concentrated over different areas.  

Therefore, without MPR heads you need to match the flow of each head to its arc to make sure the entire zone has the same precipitation rate (otherwise you will get dry spots).

The Type of Sprinkler Head Matters: 
Different sprinklers have different precipitation rates, which means that different sprinkler types need to be run for different lengths of time to deliver the necessary amount of water to your lawn.  This is where most people get it wrong.  For example, running a spray zone for 15 minutes can put down more water on your lawn than running a rotor zone for 60 minutes!  This is also why you generally cannot mix different types of sprinkler heads on the same zone (there are exceptions where this mixing of heads is done on purpose, such as when different areas of a zone need more/less water than the rest of the zone, but for most systems this should be avoided).

·    Spray nozzles (such as the Rainbird MPR nozzles), use a constant fan of water and put down water the fastest, with a precipitation rate (sometimes matched) of 1.5 – 3.0 inches (38 – 75 mm) per hour, depending on the spray radius and coverage design. Generally, these can run up to 15 minutes per watering.

·       Rotary Nozzles (such as the Hunter MP Rotator), use multiple rotating streams of water to put down water much slower, with a matched precipitation rate of 0.4 – 0.8 inches (10 – 20 mm) per hour, depending on the brand, model, and coverage design.  Generally, these can run up to 60 minutes per watering.

·       Rotors (such as the Hunter PGP Ultra), use a single rotating stream of water and also put down water much slower, with a precipitation rate (typically non-matched) of 0.2 – 0.8 inches (5 – 20 mm) per hour, depending on the spray arc, brand, spray radius, nozzle flow, and coverage design. Generally, these can run up to 60 minutes per watering

·       Drip Irrigation (such as Rainbird Xeri products), put down water the slowest and are typically used for watering plants rather than lawns, with a precipitation rate measured in gallons per hour. Drip irrigation can run 1 or more hours per watering.

 

Directly Measuring Precipitation Rate:
So how much water do YOUR sprinkler put down at once? While a good irrigation professional will be familiar enough with the different coverages, types, brands, and models of sprinklers used by your irrigation systems to calculate each zone’s precipitation rate, you can also directly measure this for yourself by using measuring cans through the following steps:

1.       Place several tin cans (or any watertight containers that do not have a tapered profile) across the area being watered by a single zone of your irrigation system and run that zone for 15 minutes.

2.       Measure the depth of water in each can and calculate the average depth.
 
(the amount may normally vary up to 2x between each can, but differences beyond this might indicate uneven coverage.  If this is the case, your local certified irrigation technician can help modify your system for more even coverage) 

3.       Take this average and multiply it by 4 to find the zone’s precipitation rate per hour

4.       Repeat this process for each zone of your irrigation system

Once you have the precipitation rate of your zone, you can divide your total weekly water requirements by the precipitation rate to figure out how many hours per week you need to run that zone.

\frac{Weekly Water Needs}{Zone Precipitation Rate}=Weekly Zone Run Time

Example: with grass needs 1.2 inches of water per week and a zone of MP Rotators has a precipitation rate of 0.4 in/hr

\frac{1.2}{0.4}=3 hours per week

4) How often should you water your lawn?

Now that you know how many hours per week you should to run your irrigation zones (see above section), you now need to figure out how much water to put down during a single watering, which then determines how many times a week you should water your lawn.  

The goal here is to put down as much water as possible without losing water to runoff or movement below the lawn’s root zone.  Therefore, for each zone it is best to consider the following:

Soil Type: 
How water is stored in and moves through the soil depends mainly on the size of the particles that make up the soil5Logsdon, S. D. (2008). Soil science: Step-by-step Field analysis. American Society of Agronomy and Soil Science Society of America.  The easiest way to tell which type of soil you have is to dig up a small portion of your lawn’s root zone and see how it feels:

·       Clays (feels sticky when wet) are made up of very small, tightly packed particles, so water moves very slowly through it.  Therefore, you need to water lawns with clay soil very slowly (0.2 inches per hour) otherwise the ground will saturate and any extra water will form runoff or evaporate and be wasted.  If you see runoff or ponding water, you are putting down water too fast!  

       Also, since clay holds onto water very well and can lead to a “soggy” lawn if too much water is put down, you can often water about 15% less with clay soils than with other soils.

·       Sands (feels coarse to touch) are made up of larger particles that water moves through quickly.  These soils can often handle a watering rate of 0.6 inches per hour or higher. 

However, depending on root development, you may need to water sandy soils over shorter intervals (0.2 inches at a time), otherwise the water could be pushed below the root zone of the lawn and be wasted.

·       Loams (feels like good topsoil) are made up of a mixture of particle sizes, making it the most flexible soil type and can be watered more rapidly if necessary (0.4 inches per hour), although slower watering is still generally preferable.

Root Development: 
Lawns with deeper roots have access to more soil moisture, making the lawn more drought-resistant.  If your lawn has deeper roots, you can water the area for longer and push the water deeper into the soil without wasting it.

By watering your lawn less frequently (1 – 3 times per week) for a longer duration and letting the upper level of soil dry in-between waterings, you can encourage this deeper root growth6Huang, B., Duncan, R. R., & Carrow, R. N. (1997). Drought‐resistance mechanisms of seven warm‐season Turfgrasses under surface soil drying: II. Root aspects. Crop Science37(6), 1863-1869.  However, this does not work with clay soils that are too tough for roots to penetrate deeply.

Landscape Profile: 
If you have a strong slope on your lawn, be careful!  Water will generally follow gravity along the slope of the landscape, both on the surface of the lawn and within the soil itself.  

The distance this water travels is related to both the steepness of the slope and the saturation level of the soil7Smith, R. E., Smettem, K. R., & Broadbridge, P. (2002). Basic Porous Media Hydraulics. In Infiltration theory for hydrologic applications. American Geophysical Union.  Therefore, landscapes with steep slopes should be watered slowly (0.4 inches per hour or less) so that the water is given time to be absorbed (or else it will run off).  

Also, if the soil under these slopes is clay, it may also be necessary to water in shorter intervals (0.1 inches at a time, using Cycle & Soak) to avoid saturating the surface of the soil, which also causes runoff.

With these considerations in mind, you first want to match how much water your soil can accept with how much water your sprinklers put down.  This will give you how long you can run your sprinklers at once:  

\frac{ZonePrecipitationRate}{MaximumLandscapeWateringRate}=MaximumZoneRunTime

Then you want to take the weekly length of watering time for the zone and divide it by the maximum time you can run the zone at once to figure out how many days per week you need to run this irrigation zone:

\frac{WeeklyZoneRunTime}{MaximumZoneRunTime}=WateringCyclesPerWeek

Example: zone has loamy soil (0.4 in/hr max watering rate), is on flat ground, has MP Rotators with a zone precipitation rate of 0.4 in/hr, and has a weekly zone run time of 3 hours

\frac{0.4}{0.4}=1 hour max zone run time

\frac{3}{1}=3 watering cycles per week

5) What time of day should you water your lawn?

While many people water their lawns in the mid-afternoon, this is actually the least effective time to run your sprinkler system.  Choosing the best time to turn on your sprinklers requires considering the following factors:

Evaporation:
Changes in sunlight, temperature, and wind together account for about 90% of the daily fluctuations in evaporation8Davenport, D. C. (1967). Variations of evaporation in time and space I. Study of diurnal changes using evaporimeters and grass lysimeters. Journal of Hydrology5, 312-328, so watering during the day will increase the amount of water wasted through evaporation and decrease the water actually getting to the roots.  

Since these factors are all generally at their lowest overnight, you typically want to start your irrigation system sometime before dawn.

Lawn Drying Rate:
If your lawn stays wet for too long, it can develop mold, fungal diseases (brown patches), and even insect damage.  Therefore, watering in the late evening is not recommended because your lawn will stay wet overnight without the sun to help dry out any remaining surface water.  

While factors like daytime sun exposure, soil type, and grass length should also be considered, watering in the early morning will generally provide enough time for water to soak into the soil before then being able to safely dry in the afternoon sun.  

Total Run Time: 
You should consider not only when your sprinkler system starts watering, but also when it finishes watering.  Irrigation systems run one zone after another, rather than all of them at once.  Therefore, the total run time for your sprinkler system can be calculated by adding together the run times of all the zones (as determined using the steps above).  Small systems with only 2 spray zones may only need 24 minutes to complete a watering cycle, whereas a large system with 5 rotor zones may take 5 hours to finish. 

You should try to start your system early enough so that the last zone isn’t watering within 3 hours of solar noon. Also, depending on how much you like your local paperboy, you may wish to finish watering before people are typically out and about.

A good starting point for when to turn on your sprinkler system is 2 hours before dawn, which can then be adjusted according to the above considerations.

Sample Watering Schedules

As you can see, there are a lot of considerations to take into account when crafting the perfect timing for each irrigation zone so that your lawn gets the water it needs, while minimizing any wasted water.

Below are a few sample schedules that might be useful as a starting point for putting together the irrigation timing of your system.  These schedules assume:

  • Kentucky bluegrass mix that ideally prefers 1.5 – 2 inches of water per week (of which only 75% will be irrigated in order to conserve water)
  • Average weekly temperature of 25°C (77°F)
  • 50% relative humidity
  • No rainfall during the week

This chart is just a starting point! You will want to fine-tune your timings over the year to match your unique grass mix, soil conditions, local weather, seasonal changes, and even how green you prefer your grass!

And if you would like some help programming the proper sprinkler watering times into your controller, check out our article on programming your controller [coming soon] and our videos for Rainbird and Hunter controllers below:

A few final details...

Cycle & Soak:
In the above sample zone timings, you can see that hilly landscapes have recommended “cycle & soak” times.  Cycle & Soak is a method where only a portion of the total watering time of a zone is run (“run”) before being paused for a certain amount of time to let the water soak into the soil (“soak”).  This run/soak cycle continues until the total zone run time has been “run”.  

This cycling helps prevent water loss through surface runoff (especially with clay soils).  While this cycling can easily be programmed into most automatic irrigation controllers, it can also be used on manual zones with a simple stopwatch and a plan.  See our article on Programming your Irrigation Controller for details on how to set this up with your system!

Zone Charts:
A helpful way of keeping track of the site details that determine the run times of each zone is providing a detailed description on a zone chart.  With a zone chart you can have quick access to the area being watered, the sprinklers used on that zone, and the watering schedule that you have calculated for each zone on your system.  See our article on Zone Charts for more info!

Looking for a second opinion?: 
If you are new to the world of landscape irrigation, you might have a few questions, or even just want a second set of eyes to look at the watering schedule you put together.  Remember, your local certified irrigation professional is only call away!  They might even know some unique local conditions that need special consideration.

Happy Watering!

Sources & References:

Beard, J. B. (1972). Turfgrass: Science and culture. Prentice Hall.

 

Beard, J. B., & Beard, H. J. (2005). Beard’s Turfgrass encyclopedia for golf courses, grounds, lawns, sports fields. MSU Press.

 

Carrow, R. N. (1995). Drought resistance aspects of Turfgrasses in the southeast: Evapotranspiration and crop coefficients. Crop Science35(6), 1685-1690.

 

Davenport, D. C. (1967). Variations of evaporation in time and space I. Study of diurnal changes using evaporimeters and grass lysimeters. Journal of Hydrology5, 312-328.

 

Huang, B., Duncan, R. R., & Carrow, R. N. (1997). Drought‐resistance mechanisms of seven warm‐season Turfgrasses under surface soil drying: II. Root aspects. Crop Science37(6), 1863-1869.

 

Kim, K. S., & Beard, J. B. (1988). Comparative Turfgrass evapotranspiration rates and associated plant morphological characteristics. Crop Science28(2), 328-331.

 

Logsdon, S. D. (2008). Soil science: Step-by-step Field analysis. American Society of Agronomy and Soil Science Society of America.

 

Smith, R. E., Smettem, K. R., & Broadbridge, P. (2002). Basic Porous Media Hydraulics. In Infiltration theory for hydrologic applications. American Geophysical Union.

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