Determining the correct run time for a residential sprinkler system is a common challenge, as there is no universal setting that works for every yard. Effective watering is a calculated process based on how much water plants need and how quickly your specific system delivers it. The optimal schedule is influenced by several factors, including the type of sprinkler heads, the soil composition, and the local climate. Understanding these variables helps homeowners create a precise schedule.
Understanding How Much Water is Needed
The goal of proper watering is to encourage deep root growth, making the turf more resilient to drought and heat stress. This requires applying enough water to saturate the root zone, typically the top six to eight inches of soil. For established lawns, this translates to applying approximately one to one and a half inches of water per week.
It is best to divide the total weekly amount into two or three watering sessions, as applying it in a single session is often impractical. Shallow, daily watering is detrimental because it keeps moisture near the surface, training roots to stay short where they are vulnerable to quick drying.
Calculating Run Time Based on Sprinkler Type
The actual time your sprinklers must run is determined by the system’s “precipitation rate” (PR), which measures how fast the water is applied in inches per hour. Different sprinkler head types have vastly different PRs, requiring dramatically different run times to deliver the same amount of water. For example, spray heads, used for smaller areas, have a high PR, often applying water at about 1.5 inches per hour. To apply a target depth of 0.5 inches of water, a spray head zone would need to run for approximately 20 minutes.
Rotor heads, used for larger turf areas, have a much lower PR, typically ranging from 0.4 to 0.8 inches per hour. To achieve that same 0.5-inch depth, a rotor zone might need to run for 40 to 75 minutes. Drip and micro-irrigation systems have the lowest PRs, delivering water slowly over several hours.
Adjusting Duration for Soil and Climate
Soil type dictates how quickly water can be absorbed, making the calculated run time only the starting point. Clay soil is composed of fine, tightly packed particles that absorb water very slowly but retain moisture for a long time. This soil type requires a longer total run time per session to penetrate deeply, but the frequency of watering can be reduced.
In contrast, sandy soil has large, coarse particles that drain water quickly and retain very little moisture. For sandy conditions, the total run time should be broken into shorter, more frequent watering sessions to prevent water from draining past the root zone. Climate and seasonal changes also influence the necessary run time by affecting the rate of evapotranspiration (ET). Hot, windy summer days with low humidity increase ET, requiring a longer run time to compensate for moisture loss from the soil and plants.
Implementing the Cycle and Soak Method
For many landscapes, especially those with clay soil, compacted turf, or slopes, the soil cannot absorb the total calculated run time all at once without causing runoff. The cycle and soak method addresses this by breaking the total watering duration into multiple, shorter cycles. This strategy ensures the water has time to soak deep into the soil before the next application begins.
If a zone requires 30 minutes of watering, the technique might break this into three 10-minute sessions. Each cycle must be separated by a “soak” period of 30 to 60 minutes to allow the water to infiltrate the root zone completely. The first short cycle breaks the surface tension, allowing subsequent cycles to penetrate deeper without pooling or waste.