The run time for a sprinkler system is often misunderstood. Many people mistakenly believe a single, set duration, such as 20 minutes per zone, is correct for all landscapes and conditions. This arbitrary timing is ineffective. The actual duration a sprinkler should run is determined by a simple calculation: the volume of water needed divided by the rate at which your specific system delivers it. Effective watering focuses on delivering a precise number of inches of water to the root zone, not on a generic timer setting.
Matching Watering Duration to Plant Needs and Soil Type
The proper watering duration is dictated by the needs of the plant and the physical properties of the soil. Deep-rooted plants, such as established turfgrass and shrubs, benefit from deep, infrequent watering to encourage strong root growth. The goal is to saturate the soil to a depth of at least six to eight inches for turf, or deeper for larger shrubs and trees. Watering to this depth promotes drought tolerance and a healthier plant structure.
Soil type significantly influences how quickly water must be applied to reach the target depth. Sandy soils have a high infiltration rate and absorb water quickly, but they retain less moisture. Clay soils have a low infiltration rate, meaning water must be applied slowly to prevent runoff, but they hold moisture for much longer periods. For example, one inch of water may penetrate sandy soil by one foot, but the same amount might only penetrate heavy clay soil by four to six inches.
Determining Your Sprinkler System’s Water Output Rate
The next step is establishing the Precipitation Rate (PPR) for each sprinkler zone. This rate measures how many inches of water your system applies per hour. Different sprinkler head types have vastly different output rates; high-flow spray heads apply water much faster than low-flow rotating nozzles or drip systems.
The most accurate method for finding your system’s PPR is the Catch Cup Test. This involves placing five to ten identical, straight-sided containers, such as tuna cans, randomly across a single irrigation zone. Run that zone for a fixed period, typically 15 or 20 minutes, then measure the average depth of water collected in all the cups.
To calculate the hourly PPR, convert the measured depth into an hourly rate. For instance, if the system ran for 15 minutes and the average collection was 0.25 inches, multiply that number by four to find the hourly rate of 1.0 inch per hour. Once the PPR is known, you can calculate the run time needed to deliver the required volume of water. If your target is 0.5 inches of water and your system applies 1.0 inch per hour, the correct run time for that zone is 30 minutes.
Why Cycle and Soak Prevents Water Runoff
Using the total run time calculated from the PPR in a single session often leads to water waste. This is true for heavy clay soils or sloped areas, which have a limited soil infiltration rate—the speed at which water can be absorbed. When the sprinkler system’s application rate exceeds the soil’s infiltration rate, the water pools on the surface and runs off.
The Cycle and Soak method solves this problem by breaking the total calculated watering duration into two or three shorter segments. For example, a total 45-minute run time could be split into three 15-minute cycles. Between each cycle, a 30 to 60-minute pause is introduced, allowing the water from the first cycle to fully soak into the deeper soil layers.
This technique ensures the entire volume of water is absorbed by the soil, maximizing the amount that reaches the plant roots. The brief initial cycle breaks the surface tension of the dry soil, making the ground more receptive to subsequent applications. This practice promotes deeper moisture penetration and minimizes runoff, especially where heavy soils make deep watering challenging.
Setting the Right Watering Schedule and Frequency
Once the correct total duration is determined and segmented into a Cycle and Soak schedule, the final step is establishing the most effective time and frequency for application. The optimal time for watering is in the early morning, ideally between 4:00 AM and 8:00 AM. Watering during this window minimizes water loss to evaporation, as temperatures are lower and winds are calmer.
Morning watering allows the plant foliage to dry completely before nightfall, which reduces the risk of fungal diseases. Midday watering is inefficient due to intense heat. Late evening watering leaves the lawn damp overnight, creating an environment favorable for pathogens.
The frequency of watering should align with the principle of deep, infrequent applications. Established lawns require one to two inches of water per week, best applied in one or two deep sessions, not daily shallow bursts. This encourages roots to grow downward in search of moisture, making the plants more resilient to heat and drought. Adjustments are necessary throughout the year, with a reduced schedule during cooler spring and fall and increased frequency during peak summer heat.