Determining how long a sprinkler should run is a common point of confusion for maintaining a healthy lawn. There is no simple, universal answer because the correct duration depends entirely on your specific system and local environment. Focusing on a set time often leads to inefficient watering and unhealthy turf. Instead, the focus must shift to volume: determining how many inches of water your lawn needs and how long your sprinkler takes to deliver it. This volume-based approach is the foundation for water conservation and achieving deep, resilient turf roots.
Focusing on Depth, Not Duration
The objective of irrigation is to achieve deep moisture penetration into the soil, not just wet the grass blades. For most established turfgrass, the goal is to saturate the root zone, typically six to eight inches deep. This encourages roots to grow downward, making the lawn more resilient to heat and drought by accessing deeper water reserves.
Frequent, short bursts of water are detrimental because they only moisten the top inch or two of soil. This shallow watering trains roots to stay near the surface, making the grass highly susceptible to drying out and increasing disease risk.
The necessary water volume varies significantly depending on the soil composition. Clay soil, with its small, tightly packed particles, absorbs water slowly but holds moisture for a long period once saturated. This requires less frequent, but longer, watering sessions, often utilizing a “cycle and soak” method to prevent runoff.
Sandy soil, composed of larger particles, drains water quickly and holds less moisture. This necessitates more frequent, yet shorter, watering sessions to avoid deep percolation past the root zone. Loam soil, an ideal mix of sand, silt, and clay, offers the best balance, requiring about one inch of water to reach the six-to-eight-inch depth. Understanding your soil type is the first step in setting an effective sprinkler duration.
Calibrating Your Sprinkler System
To determine the exact run time needed to deliver the target volume of water, you must first calibrate your sprinkler system. This involves calculating its precipitation rate, the speed at which your sprinklers apply water (measured in inches per hour). The simplest method for this calculation is the “catch can” test.
Begin by placing four to ten straight-sided containers (such as tuna cans) randomly within a single irrigation zone. Place them in various spots to account for uneven coverage. Run the sprinkler system for a measured period, typically 15 minutes, timing the session accurately.
After the run time, use a ruler to measure the depth of water collected in each can, recording the measurement to the nearest eighth of an inch. Calculate the average depth collected by summing all measurements and dividing by the number of cans. To convert this 15-minute average into the precipitation rate (inches per hour), multiply the average depth collected by four.
For example, if your average collection is one-quarter inch in 15 minutes, your system’s precipitation rate is one inch per hour.
Different sprinkler heads have vastly different rates, making a test mandatory. Spray heads, which produce a fine mist, often have a high precipitation rate, sometimes applying over one and a half inches per hour. Rotary heads, which distribute water in slow, rotating streams, are slower, applying between one-half and one inch per hour.
Once you know your system’s rate and your target volume (e.g., one inch), you can calculate the exact run time by dividing the target amount by the application rate. A one-inch-per-hour system would run for sixty minutes to deliver one inch of water.
Watering Schedules: Frequency and Timing
Once the correct run time is calculated, the final step is establishing the proper schedule, focusing on frequency and timing. The core principle is the “deep and infrequent” rule, which promotes a strong, deep root structure. Instead of watering daily for short periods, aim to deliver the full volume of water in one or two sessions per week during summer, adjusting based on soil type and weather.
The best time to run sprinklers is early morning (4:00 AM to 10:00 AM). This timing minimizes water loss to evaporation because temperatures are cooler and winds are calmer. Watering during this window also allows grass blades to dry completely as the day progresses, reducing the risk of fungal diseases.
The grass itself is the ultimate indicator of when to water, not the calendar. Watch for early signs of drought stress, such as the turf taking on a dull, bluish-gray color. A simple test is to walk across the lawn; if the grass blades do not spring back quickly and your footprints remain visible, it is time to water. These visual cues adjust your schedule seasonally.