“How long should I run my sprinklers?” This is a question that I get every year. The problem is I can’t tell you in a simple sentence that you need to run them for “X” number of minutes. There are just too many variables to make a blanket statement like that. But without getting too nerdy about it I can tell you how to determine the length of time they should run pretty quickly. It won’t be 100% of the answer but it is a good place to start.
I want to discuss turf zones. We can talk about flowers, pots, and drip irrigation at another time. There are a few givens we need to understand:
- Tall fescue lawns need 1-2 inches of water per week through rain and/or irrigation. The higher end during the heat of summer if you elect to keep your lawn green.
- Clay soils (like ours) have a percolation (ability to allow water to penetrate) rate of about .25” per hour
- It is best to water deeply and infrequently
- We define deeply as watering to a depth of 8”
- To water 8” deep we need .5 inches of water
I want to note also that there are exceptions to all of these rules but these are good guidelines most of the time.
Related Read: A Sprinkler System That Is Definitely Smarter Than a Fifth Grader
Calibrate Your Sprinkler
To calibrate your sprinkler (hose or in ground system) you need to determine how much water it delivers over a given time. Here is an easy way to do that:
Take a tuna fish can or cat food can and set it in the middle of the water pattern. Let that zone or the sprinkler run for 10 minutes and measure how much water is in the can. You are looking for .25” of water. Now adjust your time until you can deliver that .25” inch. Do this for each zone, the small spray heads may be only 3-4 minutes and big full circle rotor zones may be 30-45 min.
Water Deeply
Use a rain/soak/rain pattern to water deeply. When you water you don’t want to water more than .25” in an hour because the soil just can’t absorb it and it will run off down the storm sewer wasting water and money. But we want to water .5” each time we water the lawn because that will wet the soil profile the full 8” deep. If you are pulling a hose you really can’t do this so just water until you have that .5” of water and then move your sprinkler. If you have an automatic system, you can set two start times that run back to back in the early morning. For example, your first start time is at 3:00 and it takes 1.5 hours to run through all of your zones and deliver that .25” of water. Then set a second start time at 4:45 (so they don’t overlap). Now you will have watered deeply and as efficiently as possible.
Related Read: The Homeowner’s Complete Sprinkler System Checklist
Water Infrequently
With the sprinkler calibrated like we did in steps 1 and 2, we can set our schedule. We know we water .5” each day we water and we know the lawn needs 1-2 inches of water between rain and irrigation. We also know that we want the lawn to dry down between waterings to help promote healthy rooting. Given these factors we can set the sprinkler to run on Monday and Thursday (or Tue. and Fri.) and know that we delivered 1” of water for the week. This is a good place to start in cooler weather. When the lawn starts to stress from heat we will need more water and then we can go to Mon., Wed., Fri. and know that we are delivering 1.5” of water. This will get you through most summers. But when we get that 100 degree August blast furnace, you may need to go to an every-other-day schedule to deliver the full 2” of water. NOTE: This is without any rainfall. You should have a rain sensor and or a rain gauge to know how much water Mother Nature is helping with.
So as you can see, there are several variables in setting your run times for your sprinklers but with a little effort you can set your system to run efficiently and effectively and not pay for water you that isn’t getting into the soil.
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