The primary objective of setting sprinkler run times is to deliver a precise volume of water that meets the needs of the landscape while preventing wasteful runoff or deep percolation below the root zone. Achieving this balance requires homeowners to move beyond arbitrary timer settings and instead use a systematic approach based on the specific conditions of each watering zone. The total time a sprinkler runs is a product of the landscape’s water requirement and the system’s ability to apply that water effectively.
Understanding Your Zone’s Requirements
The initial step in setting a sprinkler run time is to identify the precise water volume your landscape requires. This target volume is highly dependent on the type of plants being watered. For instance, shallow-rooted turf grass requires more frequent, yet shallower, water applications than deep-rooted shrubs or trees, which thrive on less frequent, deeper watering events. Grouping plants with similar needs into the same irrigation zone is important for efficiency.
The soil composition in the zone also significantly influences how much water can be applied at once. Clay soil absorbs water slowly but holds it for a long time, meaning it needs a low application rate to avoid pooling and runoff. Conversely, sandy soil absorbs water quickly but retains very little, necessitating more frequent watering to replenish the rapidly draining moisture.
Environmental factors such as sun exposure and slope further modify the water demand. Areas receiving full, intense sunlight lose water more rapidly through evaporation and plant transpiration than shaded areas, increasing the overall water requirement. Similarly, sloped areas have a higher tendency for water runoff, which limits the amount of water that can be effectively delivered in a single application.
Converting Water Needs Into Minutes
Once the target water volume is established, it must be translated into a specific run time using the sprinkler system’s “precipitation rate.” This rate, expressed in inches per hour, measures how quickly the sprinklers apply water. The calculation is to divide the required water volume (inches) by the precipitation rate (inches per hour) to find the total minutes the system must run.
The precipitation rate is determined by the specific type of sprinkler heads used in the zone. Standard spray heads typically have a high precipitation rate, sometimes applying water faster than the soil can absorb it. Drip irrigation systems, however, have a much lower application rate, delivering water slowly and directly to the plant root zone.
A simple way to find your system’s actual precipitation rate is by conducting a catch-cup test, placing several straight-sided containers within the zone to collect water over a set period. By measuring the average depth of water collected and dividing it by the run time, you can determine the zone’s application rate in inches per hour. This measured rate provides the accurate figure needed for the run-time calculation.
Maximizing Soil Absorption
The total run time calculated from the precipitation rate often cannot be applied all at once without water loss. Applying the full duration continuously can cause the water to pool on the surface and flow away from the intended area. This issue is addressed by implementing a “Cycle and Soak” strategy, which breaks the total watering duration into smaller, repeated intervals.
For example, a total run time of 30 minutes might be split into three 10-minute cycles. After the first cycle, the system is paused for a soak period, typically 30 minutes to one hour, allowing the initial application to infiltrate the soil. This application helps break the surface tension of the soil, making it more receptive to subsequent watering.
The following cycles apply more water, which is then absorbed deeper into the root zone because the soil has had time to process the moisture from the previous application. This technique ensures the water penetrates below the surface where it is less likely to evaporate and is more accessible to plant roots, significantly improving watering efficiency and plant health.
Seasonal Adjustments to Run Time
The total run time established using the precipitation rate and cycle-and-soak method is generally considered the 100% setting for peak summer water demand. Plant water needs fluctuate significantly throughout the year based on changes in weather. Instead of manually recalculating and changing the run time for every zone, most modern controllers have a “seasonal adjustment” feature. This feature, sometimes called a water budget, allows the user to increase or decrease the base run time for all zones by a single percentage multiplier.
During cooler spring and fall months, when less water is lost to evaporation, the run time may be reduced to 70% to 90% of the summer peak. This reduction reflects the lower demand for plant moisture without requiring a complex reprogramming of the controller.
In the winter or during periods of heavy rainfall, this percentage can be lowered substantially, sometimes to 10% or 20%, or the system can be turned off entirely. Using the seasonal adjustment percentage is a simple, effective method for dynamically matching water application to the landscape’s current evapotranspiration rate, which conserves water and prevents overwatering.