The following chart answers these questions with a suggested weekly schedule for spray-head irrigation. It assumes heavy clay soils common to most of IRWD's service area.
Generally, these are the MAXIMUM times you will need for full sun areas. Start with this schedule and increase the times only if your plants show signs of stress. If stress occurs only in isolated areas, check the operation of your irrigation system before increasing the time.
* By "cycling" the irrigation controller to turn on for the recommended number of minutes an hour apart, deeper watering and healthier root growth are gained, while runoff is reduced.
** In September, plants' water needs drop by approximately 30 percent even if the temperature is hotter, because the days are shorter, so evaporation decreases. Also plants begin to go into a dormant phase where they need less water. In some years, humidity is also higher, increasing your level of discomfort, but decreasing plants' water needs as it slows the rate of evaporation. This rapid drop in water needs will continue in October and November.
*** The percent option, either a button or a dial, permits the watering run times for all electric valves managed by a controller to be increased or decreased with just one adjustment by percentage.