The question of how long to run a sprinkler system is not answered with a single minute count, but requires a calculation based on your specific irrigation equipment and local environment. Determining the correct duration involves understanding the fundamental goal of watering, measuring the system’s output, considering the soil type, and applying an efficient watering technique. By following a structured approach, you can move past guesswork and establish a highly effective watering schedule for a healthier landscape. This customization prevents wasted water and protects plant health.
Understanding the Goal of Deep Watering
The primary objective of any irrigation schedule is to encourage the deep growth of plant roots. For most healthy turf and landscape plants, this root zone should extend to a depth of four to eight inches into the soil profile. Watering to this depth promotes a robust root system capable of accessing moisture deeper in the soil during periods of dry weather. Plants with deep roots are naturally more resilient to drought and high temperatures.
A common error is watering frequently for short periods, which only wets the top inch or two of the soil surface. This habit trains the roots to stay shallow, making them vulnerable to rapid drying and heat stress. Shallow root systems encourage disease and weed growth. Deep, infrequent watering allows the soil to dry slightly between cycles, pulling oxygen into the root zone and strengthening the plant.
Calculating Your Sprinkler Output Rate
Before determining the total run time, you must first measure the precipitation rate of your specific sprinkler system. The most actionable way to do this is through a catch-cup test, sometimes called the tuna-can method. This test measures the volume of water your sprinklers deliver, accounting for pressure and head type.
To perform the test, place five to ten identical, straight-sided containers, such as tuna cans or specialized catch cups, randomly across a single irrigation zone. Place the containers within the sprinkler spray pattern, including areas near the heads and halfway between them, to capture the average coverage. Run the sprinkler system for a fixed, measurable time, typically 15 minutes, and then turn it off.
Use a ruler to measure the depth of water collected in each container, aiming for precision to the nearest eighth of an inch. Calculate the average depth by summing the measurements and dividing by the total number of containers used. To find the precipitation rate in inches per hour, multiply the average depth collected in the 15-minute test by four. This rate is the baseline for all subsequent calculations.
Adjusting Duration Based on Soil Type
The soil composition in your landscape dictates both how quickly water can be absorbed and how much water it can hold in the root zone. Once you know your system’s output rate, you must modify the total watering time based on whether you have sandy, loamy, or clay soil.
Sandy soils have large particles and high infiltration rates. Water drains quickly and has a low water-holding capacity. These soils may need less water applied at once, perhaps aiming for a total depth of one inch or less, but the watering frequency may need to be slightly higher.
Clay soils, conversely, have small particles and a slow infiltration rate, but they hold water tightly once saturated. Water applied too quickly results in immediate runoff and waste. Because the soil retains moisture well, it requires less frequent watering overall. Landscapes with clay soil may require a total application depth of 1 to 1.5 inches per session to soak the entire root zone, but this application must be delivered slowly.
Loamy soil represents a near-ideal balance of sand, silt, and clay, offering good drainage while maintaining adequate water-holding capacity. This soil type is the most flexible, requiring moderate run times to apply about one to 1.25 inches of water to achieve the deep watering goal.
Implementing the Cycle and Soak Method
The cycle and soak technique is a highly effective application method that prevents wasted water and is particularly beneficial for clay soils or sloped areas. Instead of running the sprinklers for the total calculated duration at one time, this method breaks the watering into multiple, shorter segments with a rest period in between. This allows the water applied in the first segment to fully infiltrate the soil, rather than pooling on the surface and running off.
For example, if a zone requires 45 minutes of total watering time, the cycle and soak method would divide this into three 15-minute cycles. A rest period of 30 to 60 minutes between each cycle allows the initial water to soak down into the root zone. The first cycle breaks the surface tension of the soil, and subsequent cycles push the moisture deeper. Monitoring the soil for the first signs of runoff during the initial cycle can help determine the maximum duration for each segment before the soak time is necessary.