Figuring out how long to water

Getting Started:

The Inland Valley Garden Planner provides useful irrigation schedules for different plants and plant palettes.  These charts provide recommendations in units of inches or partial inches of water.  To make use of these recommendations, those recommendations must be converted to number of minutes to run each zone of your irrigation system.  Because the rate at which each zone puts out water varies based on both the layout of the system and the products used, it takes some measurements to get good numbers.  Not to worry, we explain and walk you though the whole process below and provide some handy calculators to do the math for you!

Why do we provide Irrigation Recommendations as Inches of Water?

The Inland Valley Garden Planner provides irrigation recommendations as “inches of water”.  You can think about this measurement as an inch deep of water covering the entire irrigated area in your yard or landscape.   We provide irrigation recommendations in inches, instead of recommending how long to run your irrigation system, because the flow rate at which different irrigation systems provide water varies greatly.  Even within the same irrigation system type, like spray systems, different spray nozzles and sprinkler layouts can cause significant differences in how fast water flows in any specific irrigation zone on a property.  Inches of water is a more uniform measurement that can be applied to any irrigation system, on any property.

Here are a few useful terms to help apply the Inland Valley Garden Planner irrigation recommendations to your own irrigation system.  The rate at which an irrigation system puts out water in inches is the “precipitation rate” and is measured here as inches per minute.  A “zone” refers to an area of your yard that is irrigated with one single valve.  A “hydrozone” refers to an area in which all plants have similar water needs. Setting up hydrozones is the most water efficient and simple way to irrigate your yard, and it also results in the best plant health.

For the reasons listed above, we provide recommendations for the volume of water (in inches) required to properly irrigate a zone of plants, and provide additional resources to help you determine the schedule and precipitation rate for each zone of your irrigation system.  Once you know how much and how often a zone of your yard needs water (supplied by the schedule charts in the Inland Valley Garden Planner), and the precipitation rate of that zone, you can calculate how long you will need to water (also known as run time) for each zone of your irrigation system for different seasons of the year.

How can I convert the “inches of water” recommendations into a usable irrigation schedule for my irrigation system?

Depending on the type of irrigation you have in your yard (spray, rotor, or drip irrigation), different methods are available for you to use to calculate your irrigation schedule.  Some require a bit more math and some a bit less – use whatever method is best for you.  Remember, if you live within the area served by the Chino Basin Water Conservation District (find information here), and you have a functional irrigation system, you can sign up for a free “Irrigation Efficiency House Call,” and as part of the service, we will calculate precipitation rates for you and provide you with irrigation timer recommendations.

To use the calculators (below):

Before starting, briefly run the irrigation for the areas you will be measuring to make sure there are no clogged or broken sprinklers or leaks.  If anything is broken or clogged, fix it before testing.  You can check for leaks in drip lines buried in mulch by running the system and walking the area both looking for visual leaks, or for smaller leaks, listening for a hiss or other unusual sounds.  We offer two different calculators which can help people with different irrigation setups.  Read through the rest of this page before choosing which approach is best for you.  Don’t get intimidated!  We’ve also provided links to step-by-step examples with pictures.

If you have a spray or rotor system, you can determine the precipitation rate using a simple “catch can” or “jar test” method. The simplest method is to use 12 to 24 jars with wide mouths and straight sides, such as cat food cans, tuna cans, or pint-size wide-mouth mason jars.  Many containers will work, as long as the opening is the same size as the rest of the container and you have a large number of matching containers (see image).  One convenient option is to buy a 12-pack of wide-mouth pint size (NOT quart size) mason jars.  To test your precipitation rate, place the identical jars or cans in roughly a grid in one zone of your yard, ensuring that some cans are placed close to the sprinklers and that some are placed in the center of the irrigation areas.  Run the corresponding zone of your irrigation system for 10 minutes. After 10 minutes, measure and record the depth of water in each container (in inches or part-inches) by using a ruler either along the side of the jar, or dipped into the can.  Use the chart below to convert those fraction measurements into decimal measurements.  Then, enter that information into the calculator below.  Click here for a step-by-step example.  Note: This is a simplified process from a professional irrigation audit or catch can test, but is a simple way to get a good idea of precipitation rate and run time for home gardeners.

Converting eighth-inches to decimals

Inches (in eights)inches (decimal)
7/80.875
6/80.75
5/80.625
4/80.5
3/80.375
2/80.25
1/80.125
Use this table to convert your ruler measurements to decimals to input into the table below.

Irrigation Run-Time Calculator by Jar Test

0minutes
* Required

If you have a drip irrigation system, or if you want to use an alternate method to test your spray or rotor system, you can use your water meter to get your average precipitation rate for each zone.  This method requires additional math, because it relies on the meter reading and the area (in square feet) of the irrigation zone you are testing.  First, use a measuring tape or measuring wheel to get a measurement of the total area irrigated by the valve you are testing, in square feet.

Next, find your water meter box, and carefully open it with gloved hands (black widow spiders often live in them).  You will need a screw driver or other tool to open the lid.  Check the underside of the lid and the inside of the box for spiders to make sure the area is safe.  Then, pull up the faceplate of the meter to reveal the numbers.  You may need to clean off the faceplate to clearly read the numbers.  Record, in cubic feet, the current numbers shown on the meter before starting your irrigation valve (this is referred to as “beginning meter reading”).  Run your irrigation system and record the how long it ran.  We recommend at least five minutes for sprays, ten minutes for rotors, and fifteen minutes for drip.  Record the new number shown on the meter after running the valve for the area you are measuring. This is referred to as “End meter reading”.   Enter the information into the calculator below.  Click here for a step-by-step example.

Irrigation Run-Time Calculator by Meter Reading and Area

Note: All fields must be entered to display correct results

0minutes to apply desired amount of water
* Required