The time to run an oscillating sprinkler is not a fixed number of minutes, but the duration required to deliver a specific volume of water to your lawn. Efficient watering focuses on providing a deep soak to encourage robust root development, making the turf more resilient to drought and heat stress. Finding this precise run time accounts for the varying output of your sprinkler. This approach avoids shallow, frequent watering that promotes weak root systems and wastes water.
The Goal: Establishing Deep Watering Requirements
The objective of effective lawn irrigation is to saturate the soil deeply but infrequently. This technique encourages grass roots to grow downward, seeking moisture deeper in the soil profile. Roots that only grow near the surface quickly dry out and suffer damage during periods of high heat or when watering is skipped.
For most turfgrass varieties, the target is to soak the soil six to eight inches deep during each watering session. This saturation depth requires applying approximately one inch of water across the lawn area. Delivering one inch of water ensures the moisture reservoir sustains the grass for several days, depending on the climate and soil type. This practice maximizes the interval between watering sessions and reduces the risk of disease.
Calculating Oscillating Sprinkler Run Time
Since no two oscillating sprinklers apply water at the same rate, the only reliable way to determine run time is by measuring its output. This is achieved using a catch cup test. The test determines the precipitation rate—how quickly your sprinkler delivers water—which is then used to calculate the time needed to reach the one-inch goal.
To perform this test, use several straight-sided containers, such as tuna cans, placed randomly throughout the sprinkler’s spray pattern. The positioning should cover areas both close to the sprinkler and near the edge of the throw to ensure an accurate average measurement. Run the sprinkler for a predetermined period, such as 15 or 20 minutes, and record the exact time.
After the test run, measure the depth of water collected in each container and calculate the average depth across all cups. For example, if you ran the sprinkler for 15 minutes and collected an average of 0.25 inches, you can calculate the total time needed to reach one inch. Dividing the target depth (1 inch) by the measured depth (0.25 inches) and multiplying by the test time (15 minutes) results in 60 minutes of total run time. This duration is the time required to achieve the deep watering goal for your lawn.
Modifying Duration for Soil and Climate
The calculated run time is the total duration required, but this total may need to be broken into shorter segments based on soil type and landscape. Soil composition influences the rate at which water can be absorbed, known as the infiltration rate. Sandy soils absorb water quickly, meaning the full duration can often be applied in one continuous session.
Conversely, clay soils have smaller pore spaces and a slower infiltration rate, often leading to water pooling or running off before it can soak in. For these heavier soils or sloped areas, the total run time should be divided into multiple shorter cycles with rest periods. This is known as the “cycle and soak” method. For example, you might run the sprinkler for three 20-minute cycles, allowing a 30 to 60-minute break between each to let the water fully infiltrate the root zone.
Climatic conditions also affect the water reaching the soil, primarily through increased evaporation. High temperatures, low humidity, and wind accelerate the rate at which water droplets evaporate before they hit the ground. Watering during the early morning, when temperatures are cooler and wind is calmer, minimizes this evaporative loss. In extremely hot or windy conditions, you may need to slightly increase the total calculated run time to compensate for unavoidable water loss.