The timing and duration of your irrigation system’s run time are fundamental to maintaining a healthy landscape while conserving water. Efficient watering delivers the correct amount of moisture only when the soil requires replenishment, not every day. The goal is to match the water supply to the plant’s needs and the soil’s capacity. This prevents wasted water from runoff or deep percolation below the root zone. Optimizing your system begins with understanding the relationship between watering frequency and duration.
Establishing the Base Schedule: Deep and Infrequent
The most effective strategy for established lawns and plants is a deep and infrequent watering schedule. Shallow, daily sprinkling is detrimental because it promotes weak, shallow root systems that are highly susceptible to heat and drought stress. Deep, infrequent irrigation encourages roots to grow downward, seeking moisture deeper in the soil profile where temperatures are cooler and water is more stable. This deeper root growth makes the plant more resilient and better able to withstand periods of high heat or reduced rainfall. For established turf, “infrequent” often means watering only once or twice per week, depending on the climate.
The most accurate way to determine when the next watering is needed is by monitoring the soil directly. Use a simple tool like a long screwdriver or a probe to check moisture depth manually. The probe should slide easily through moist soil but meet resistance when it hits dry soil. Aim to water before the top 6 to 8 inches of soil become completely dry. Visual cues, such as a dull, grayish-green color or footprints remaining in the lawn, also indicate the beginning of plant stress.
Calculating Run Time Based on Soil Composition
The duration of your irrigation session is determined primarily by the soil’s composition. Different soil types have varying infiltration rates, which is the speed at which water soaks in, and distinct water holding capacities. The goal is to apply roughly 0.5 to 1 inch of water per watering session to soak the root zone without causing runoff or waste.
Clay soil has a very low infiltration rate because its particles are tiny and tightly packed. If water is applied too quickly to clay, it will pool and run off, meaning the plant receives little benefit. Clay soil requires a much longer total run time to deliver the necessary inch of water, but this must be broken up into short cycles using a technique called “cycle soaking.”
Cycle soaking involves running the irrigation for a short period—typically 5 to 10 minutes—until runoff begins. The system then pauses for 30 to 60 minutes to allow that water to soak in, and the cycle is repeated until the total desired volume is delivered.
Conversely, sandy soil has a high infiltration rate due to large particles, allowing water to drain very quickly. Sandy soil requires shorter run times and may need to be watered slightly more frequently within the “infrequent” schedule, as it holds less water overall.
To accurately calculate your system’s run time, you must first know its precipitation rate, which is the amount of water it delivers over time. A simple “catch can test” involves placing several flat-bottomed containers, such as tuna cans, across a zone and running the system for a set time, like 10 or 15 minutes. By measuring the average water depth collected, you can calculate the minutes required to deliver a target of 0.5 to 1 inch of water.
Seasonal Adjustments and Monitoring
The base schedule established by the deep and infrequent principle and the soil-based run time is not static; it must change with the seasons and local weather conditions. Plant water needs increase significantly in hot summer months due to a higher rate of evapotranspiration (ET), which is the combined water loss from soil evaporation and plant transpiration. In summer, you should increase the frequency of your deep watering sessions—moving from perhaps once a week to every three or four days—while generally keeping the duration (the amount of water applied) the same.
As temperatures cool in the spring and fall, the ET rate drops, and the frequency of watering should be reduced. During these milder months, your system may only need to run once a week or even less, especially if rainfall is consistent. Many modern irrigation controllers offer a “seasonal adjustment” feature, allowing you to increase or decrease the program run times by a percentage without reprogramming the entire schedule.
Monitoring the environment remains necessary, even with automated systems. Rain sensors or weather-based smart controllers can automatically pause the system after significant rainfall, preventing overwatering. The most reliable indicator of your plant’s water needs is visual inspection: look for wilting or a change in the plant’s color. Adjusting the schedule based on these observations ensures your landscape receives water only when needed.