Irrigation Run Time Chart Instructions
“Inches of water needed” is how much water you want total. If you’re unsure for a particular plant or turf, it can be estimated from your local ET rates from the chart. The PR (precipitation rate) can be acquired from the precipitation rate charts.
For example, assume your plant requirement is. 18 inches per day and your PR rate is 48 inches per hour. Since there is not. 18 inches per day and .48 PR, use the closest figure. In this example, you would use .20 inches per day and .50 PR. Selecting the figure where these two figures intersect gives you 24 minutes per day of run time needed. If your city allowed only three watering days a week, then you would multiply the 24 minutes times 7 days in a week to get 168 minutes of run time for the week. Finally, divide the 168 by 3 days to arrive at 56 minutes of run time three times a week.
Remember, this is a good starting point for water scheduling, however, final adjustments may need to be made (upon observation) to arrive at a more accurate figure.