How Long Should You Leave Your Sprinklers On?

While a sprinkler can provide efficient watering to your garden, how well your plants thrive depends on how long you run the sprinklers. Insufficient water often means brown, curled-up grass, while excess water translates to a soggy garden that becomes a breeding ground for fungus and pests.

How long you should leave sprinklers on depends on the kind of soil (clay, loamy, or sandy), the type of grass (cool-season vs. warm-season), when you give water (morning vs. evening), the amount of rainfall received, and the sprinkler’s output. Generally, lawns need 1.5 inches of water per week. 

As you can see, there are a number of factors to account for when determining how long you should run your sprinklers. Let’s take a look at each one, so that you can determine how often you should water your grass. We’ll also look at how you can set a watering schedule.  

How Often Should You Use Sprinklers to Water Your Grass?

Lawn sprinkler

To figure out exactly how often you should use the sprinklers, you first need to calculate your garden’s weekly watering needs in inches. On average, most lawns need 1-1.5 inches of water per week, but this can vary depending on the type of turf grass, i.e., whether it’s warm season or cool season, the specie of grass, and the season, i.e., dormant- or active-growth season. 

Next, figure out the sprinkler system’s output. Once you do that, calculate the duration of time you should run the sprinkler every week. All you need to do is divide the garden’s weekly water needs by the sprinkler’s water output.

For instance, if your Bermuda grass garden needs an inch of water per week and the sprinkler output is 0.5 inches per hour, you just need to run the sprinkler for 40 minutes every week.

To determine the length of a watering session, divide the sprinkler duration calculated above by the weekly watering frequency. So, if your lawn needs 40 minutes of water per week, and you plan on having two sessions in a week, then that means each watering session should be 20 minutes long. Just make sure you space the watering sessions a few days apart to allow the roots to breathe.  

Note that the watering frequency depends on the type of soil used. In some cases, you might water once a week and end up with soggy soil that encourages rot and pests. In other cases, you might water every day and end up with short roots. Generally, loamy and clay soils absorb water slowly, but they can store it for longer, which is why you can water them 1-3 times per week. Sandy soil should be watered 2-4 times a week.  

And finally, make sure you water at the right time. If you run the sprinklers when the sun is at its peak, most of the water will evaporate even before it touches the ground. Other things you should factor in here include the dryness in the air as well the wind speed, since it can direct the water away from its target.

Account for Rainfall

The calculations above don’t account for rainfall; they tell you how long you should run the sprinklers in a week without any rainfall. However, if your garden receives rainfall, it cuts down the need for supplemental irrigation.

To determine how long you need to water the lawn during the week it rains, you simply need to subtract the weekly rainfall (in inches) from the garden’s weekly watering needs.

So, if your garden needs an inch of water per week, and you receive a ½ inch of rain in that week, then your garden only needs a ½ inch of supplemental irrigation. You can determine the amount of rainfall by using a rain gauge like this one by AcuRite (on Amazon) or by checking the amount reported by the local weather station. 

Determining Your Grass Type 

There are numerous kinds of grass, each with different watering needs. While most lawns require only 1-1.5 inches of water weekly, identifying your turf can help you determine the exact amount of water you need to provide both in the dormant and active seasons. In general, cool-season grasses need more water compared to warm-season grasses. 

The growing season is also important when determining the amount of water required, since you don’t need to give the grass a lot of water in the dormant season. For cool-season grass, the active season is from spring to fall, while warm-season grass is active in the summer. Both are dormant in the winter. 

A cool-season grass like Kentucky Bluegrass needs around 1.5-2 inches of water weekly during the growing season and only half an inch during the dormant season. Meanwhile, Bermuda grass, which is a warm-season grass, needs 1-1.25 inches of water weekly during the active season and only an eighth of an inch of water per week when it’s dormant.    

How to Set a Lawn Watering Schedule

Lawn sprinkler watering grass

One of the best things about a sprinkler is the timer that you can set whenever you want. Whether you have a mechanical or a digital timer, setting up a watering schedule for your lawn is easy.

In case of a digital timer like this one from Orbit (on Amazon), here’s what you should do:

  1. Select the right zone and create a watering schedule.
  2. Choose the current time and date and set the duration the valves should remain open.
  3. Set the days for the sprinklers to switch one. 
  4. Repeat these steps for all the zones.

And if you have a mechanical timer like this one from Melnor (on Amazon), here’s how you can create a schedule: 

  1. Insert the brass pin into the hole beside the time the watering should start and choose the duration by inserting the right amount of pins.
  2. Make sure you don’t skip a hole when inserting additional pins. 
  3. Leave a hole open in case there are multiple zones in your sprinkler system. 
  4. Now, turn the dial clockwise to set the current time and turn the small black wheel counterclockwise to set the daily watering schedule.
  5. Do the same for all zones. 
  6. Remember to press down the pin in case of no watering, and switch the sprinklers on or off by setting the selector switch to ‘Auto.’ 

When’s the Best Time of Day to Water Your Lawn?

Lawn sprinkler on the grass

The ideal time to water the lawn is early morning, preferably between 6 and 10 am. If, for some reason, you can’t water the lawn during this time, water it in the evening between 4 and 6 pm, but never water your lawn at night. 

As the sun starts to go down, the evaporation decreases, but the winds might be higher at the time, taking the spray away from its target. Plus, watering at night means that the lawn will stay damp all night, potentially leading to fungal and bacterial growth. 

How to Measure the Amount of Water Being Used

To calculate the amount of water that the sprinkler system delivers in an hour, put 6 straight-sided containers (all of the same shape and size) in a part of the lawn where the sprinklers hit and switch on the sprinklers for around 20 minutes. Measure the amount of water present in each container and calculate the average across all of them.

Now, multiply the average depth by 3 to determine the inches of water delivered by the sprinkler system per hour. For instance, if the containers have an average of ¼-inch of water, your sprinkler output will come out as 1.5 inches per hour (6 x ¼).  

Alternatively, you can use the tuna can method or simply install a flow timer. For the former, put two empty tuna cans in different parts of the lawn where the sprinklers hit and let them run for 15 minutes. 

Then, just like you did with the previous method, measure the depth in each can with a ruler and take out the average of the water in the two containers. Do the same math as above to determine how long you need to run the sprinkler. 

A flow timer like this one (on Amazon) senses the water flow and keeps track of how much water is used. The flow sensors can track the irrigation in the system and send a signal to correct the flow. 

Digital Timers vs. Mechanical Timers

These days, most people use digital timers, but there are still some who prefer the mechanical option. While the former uses electronic circuits, the latter uses metal pins and gears. There are other differences between the two, too. 

A mechanical timer ensures that you water the yard more efficiently and has a few benefits. For instance, it’s more convenient compared to hand watering and helps you conserve water since you won’t forget to switch off the water. Installation is also easy and doesn’t involve any wiring. They’re also affordable and built to last. 

Meanwhile, a digital timer automates the watering schedule and helps save money and time. Plus, it allows you to program your watering schedule using a single unit. It also provides a number of benefits. For instance, you’ll never forget to water the lawn again, and you’ll get more vibrant plants. 

And you can set the timer to give water early in the morning even before the sun comes up to reduce the amount of water that evaporates and increase the amount that reaches the roots.

And finally, you can go on a vacation without worrying about who will water your plants; simply set the sprinklers and they’ll run automatically so that you can travel stress-free!

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