Determining how long a sprinkler should run in California focuses on applying a specific volume of water efficiently, rather than using a fixed time. California’s climate, marked by frequent drought and strict regulations, necessitates precise irrigation management. Calculating the correct run time involves understanding the required water amount and translating that volume based on the sprinkler system type. This approach ensures water reaches the plant roots without being wasted through runoff or evaporation.
Understanding California Water Use Regulations
The framework for outdoor watering in California includes statewide conservation rules and more restrictive local ordinances. A primary statewide regulation prohibits applying potable water to outdoor landscapes within 48 hours after measurable rainfall, typically defined as one-fourth of an inch or greater. This rule ensures landscapes rely on natural precipitation and prevents unnecessary watering and runoff.
Local water agencies and municipalities enforce additional time and day restrictions dictating when watering can legally occur. Many districts limit outdoor irrigation to specific days of the week, often based on a home’s address, and commonly prohibit watering during the hottest part of the day (e.g., 9:00 a.m. to 6:00 p.m.) to minimize evaporation. Because these local schedules and limitations vary significantly, property owners must check the specific rules published by their local water supplier before setting irrigation timers.
Determining the Right Water Volume
The duration a sprinkler runs is effective only if it delivers the correct volume of water needed to sustain the plants. Effective watering aims to apply enough water to reach the plant’s root zone, known as the effective watering depth. For turfgrass, water must penetrate six to eight inches, while shrubs and trees require deeper saturation, often between 18 inches and three feet.
The required water volume is heavily influenced by the soil type present in the landscape. Clay soil absorbs water slowly but retains it longer, meaning it requires less frequent but deeper watering. Conversely, sandy soil absorbs water quickly but drains rapidly, necessitating more frequent but shallower applications to prevent water from leaching past the root zone. Landscape managers aim to apply about a half-inch of water to moisten six inches of clay soil for a lawn, which provides a starting point for volume calculation.
Translating Volume into Run Time
Translating the required water volume into a specific run time depends entirely on the sprinkler head type, specifically its precipitation rate, which is the speed at which it applies water, measured in inches per hour. High-flow spray heads (pop-up sprays) have a high precipitation rate, often around 1.4 inches per hour, meaning they deliver water quickly. These systems require a very short run time, typically five to eight minutes per cycle, to avoid runoff.
Low-flow rotor heads or rotary nozzles deliver water in rotating streams with a much lower precipitation rate, sometimes as low as 0.4 inches per hour. Because they apply water more slowly, they require significantly longer run times, often 20 to 40 minutes in total, to deliver the same volume of water as a spray head.
Cycle and Soak Method
Using the cycle and soak method is essential for all sprinkler types, especially in California’s often dense or sloped soils, to maximize absorption and prevent runoff. This method involves breaking the total required run time into two or three shorter intervals, separated by a 30 to 60-minute pause. For instance, a total 21-minute run time should be split into three seven-minute cycles, with a soak period between each. This pause allows the water from the first cycle to penetrate the soil, making subsequent cycles more effective at reaching the deeper root zone.
Seasonal Adjustments and Watering Frequency
The frequency of watering is the main variable that changes throughout the year, driven by the concept of Evapotranspiration (ET). ET is the total water lost from the landscape through evaporation from the soil and transpiration through the plants. It is directly influenced by temperature, solar radiation, and wind. The California Irrigation Management Information System (CIMIS) provides reference ET data to help quantify the landscape’s water demand.
During the summer and peak heat months, the ET rate is highest, requiring a higher watering frequency, such as two to three times per week for lawns. As temperatures cool in the fall and spring, the ET rate decreases, and the frequency should be reduced to perhaps once or twice a week. In the winter, when the ET rate is at its lowest, watering may be necessary only monthly or less, especially if there is sufficient rainfall. Crucially, the total duration or run time per cycle often remains fixed once established, but the frequency of the watering days adjusts seasonally to match the plant’s actual water use.