Deep watering turfgrass involves applying a specific volume of water, typically one inch, to encourage robust root development. This practice helps the lawn withstand environmental stress. Determining the precise time required to apply one inch of water is not universal, as it depends entirely on the unique output rate of the sprinkler system. Finding this duration requires a simple measurement process to calibrate the equipment before calculations can be made.
The Goal of Applying 1 Inch of Water
Applying one inch of water is a targeted strategy to promote the growth of deep, resilient root systems, which are better equipped to handle periods of heat and drought. Shallow watering, which only wets the top few inches of soil, encourages roots to stay near the surface where they quickly dry out. This makes the turf susceptible to stress and damage when temperatures rise or rainfall is scarce.
A single inch of water is generally sufficient to penetrate the soil to a depth of six to eight inches, where the majority of healthy turfgrass roots should reside. When the roots are forced to grow deeply in search of this moisture, the overall plant becomes physically stronger and more capable of drawing water reserves from deeper in the soil profile. This foundational practice shifts the turf from a state of dependency on frequent, light watering to a state of self-sufficiency between less frequent, deeper applications.
Measuring Your Sprinkler System’s Output Rate
Before calculating the total watering time, it is necessary to determine the sprinkler system’s actual precipitation rate, which is often measured in inches per hour. This is accomplished by performing a simple catch-cup test within the area covered by the sprinkler zone. The test requires placing several straight-sided containers, such as tuna cans or specialized rain gauges, randomly across the lawn area. Ensure some containers are near the sprinkler heads and others are near the edges of the spray pattern.
Once the containers are in place, the irrigation system should be run for a short, set period, typically 15 minutes. After the run time is complete, the amount of water collected in each container must be measured precisely using a ruler. It is important to record the measurement from every container, as sprinkler output is rarely uniform across the entire zone due to pressure variations and overlapping spray patterns.
To calculate the average output rate, all the individual water depth measurements are added together and then divided by the total number of containers used. This average depth represents the amount of water applied during the 15-minute test period. To translate this figure into the required inches-per-hour rate, the average depth is multiplied by four. For instance, if the average depth collected was 0.25 inches, the system’s precipitation rate is 1.0 inch per hour. This calculated rate is essential for setting an efficient watering schedule.
Translating Sprinkler Rate into Watering Duration
The precipitation rate determined from the catch-cup test is the value needed to calculate the exact duration required to apply one inch of water. The basic formula for this conversion is: (Desired Depth / Precipitation Rate) \(\times\) 60 minutes = Total Watering Time. If the system’s rate was determined to be 0.5 inches per hour, the resulting calculation would be (1.0 inch / 0.5 inches/hour) \(\times\) 60 minutes, meaning the total time needed is 120 minutes, or two hours.
The total calculated time should not be applied all at once, as most soils cannot absorb water that quickly without significant runoff occurring. Instead, this total duration must be broken down into shorter, repeated sessions separated by a rest period, a technique known as cycle and soak. Applying the water in two or three shorter cycles, such as two 60-minute sessions or three 40-minute sessions, allows the water to soak fully into the soil profile between applications.
A 30-minute break between cycles is generally sufficient to allow the water to infiltrate the soil and prevents it from pooling on the surface. This cycle and soak method ensures the full one-inch volume is absorbed deep in the root zone, rather than being wasted as it flows onto sidewalks or pavement. The calculated total duration remains the same; only the application method is adjusted for absorption efficiency.
Adjusting the Watering Schedule for Soil and Weather
While the duration required to apply one inch of water remains fixed based on the sprinkler system’s output, the frequency of application must be adjusted according to soil type and current environmental conditions. Soil composition dictates how quickly water drains and how long it is retained in the root zone. Sandy soils, which have large particles and high drainage, hold less water and dry out faster than other types.
Turf growing in sandy soil may need the calculated one inch of water applied more frequently, perhaps every three to four days, especially during hot summer periods. Clay soils, conversely, have fine particles that compact easily and hold water for much longer periods. Grass in clay soil can often go seven to ten days between applications of one inch, preventing the roots from becoming waterlogged and suffocated.
The schedule must also be flexible to account for recent rainfall and current temperatures. If a heavy rain event provides a measurable amount of water, that application can be skipped or delayed until the soil moisture is depleted again. Conversely, periods of extreme heat or sustained high winds will accelerate evaporation and transpiration. This means the time between deep watering sessions may need to be shortened by a day or two to maintain turf health.