The duration of watering is not measured in minutes, but is determined by achieving a specific depth of moisture penetration into the soil. Proper lawn watering is an exercise in soil science and plant biology, not just setting a timer on a sprinkler. Understanding that you are watering the soil profile, not the grass blades, is the first step toward a healthier, more drought-resistant yard.
The Goal of Deep Watering
Achieving deep saturation of the soil is the objective of a proper watering routine. Grass roots naturally grow toward the deepest available water source. Applying water deeply encourages the root system to follow the moisture downward, developing a robust structure. Shallow, frequent watering only wets the top inch or two of soil, training roots to stay near the surface where they are easily exposed to heat and prone to drying out quickly.
The goal for most established turfgrass varieties is to drive the moisture down to a depth of four to six inches. Roots that penetrate this deep are better equipped to survive dry spells because they can access a cooler, more consistent moisture reserve. This deep-watering technique also allows the soil surface to dry out between waterings, which is important for restricting the growth of certain fungal diseases. The infrequent nature of deep watering prevents the constant saturation that can deprive roots of necessary oxygen.
Determining Soil Absorption Rate
Before determining the total watering time, understand how quickly your specific soil can absorb water without waste. The soil’s texture—sandy, loamy, or clay—dictates its infiltration rate. Applying water faster than the soil can absorb it results in runoff, which wastes water and fails to achieve deep saturation.
To determine your soil’s maximum absorption rate, run your sprinkler system and monitor for the onset of runoff. If water begins to pool or flow across the surface after 10 or 15 minutes, that duration represents the longest single cycle your soil can handle. Clay soils absorb water slowly, often requiring a cycling approach, while sandy soils absorb water quickly and can handle longer continuous runs.
This maximum absorption time will be used to divide your total calculated watering duration into smaller, manageable segments. For instance, if your soil can only absorb for 15 minutes before runoff, you will need to apply the total watering time in multiple 15-minute cycles, allowing a 30 to 60-minute break between each cycle for the water to soak in. This “cycle and soak” method ensures maximum penetration and minimal waste.
Calculating Your Specific Watering Time
The final step in determining the correct watering duration involves a calculation that combines your desired water depth with your sprinkler system’s output. The first necessary input is the application rate, which is the amount of water, measured in inches per hour, that your sprinklers deliver. This rate must be measured because it varies significantly based on water pressure and the type of sprinkler head used.
The most accurate way to measure this rate is by using a catch-can test, often performed with simple tuna cans or specialized rain gauges. Place multiple cans randomly across your lawn to capture the water distribution from your sprinkler head. Run the system for a fixed period, typically 15 minutes, then measure the average depth of water collected in all the cans.
To convert this measurement into an hourly rate, multiply the average depth collected by four. For example, if your average collection is one-quarter inch in 15 minutes, your application rate is one inch per hour. Once you have this rate, you can calculate the total time needed to achieve the target depth of four to six inches. If your goal is one inch of penetration, and your sprinkler delivers one inch per hour, your total watering duration is 60 minutes.
If your soil absorption test showed that runoff begins after 15 minutes, you would break the total calculated duration into multiple 15-minute cycles. This approach ensures the water penetrates the full four to six inches required for deep root growth while respecting the physical limitations of your soil. This calculation should be performed periodically, especially if you change sprinkler heads or notice changes in water pressure.