The Watering Index (%) is a simple way to represent and understand plant water needs. It is based on weather conditions, such as: solar radiation, temperature, relative humidity, wind, and other factors. Summer represents 100% of maximum water needed for plants. Over the course of the year the Watering Index changes to reflect the landscape’s changing need for water as climatic conditions change. As new Watering Index values are published, the controller’s water budget adjustment feature should be changed to match the current Watering Index value. The watering times for all valves controlled by one landscape controller will change by the same percentage when the water budget adjustment feature settings are changed.
Use the chart below, along with site conditions, to find the right watering index value for your yard!
Many new(er) sprinkler timers have a seasonal adjust option (or % adjust) that you can use. To do so, first program your sprinkler times for summer conditions (100% seasonal adjustment factor). You can then just use the seasonal adjust feature to adjust the watering index to the appropriate percentage. For example, if it’s October, you use a watering index of 50-60% and your sprinkler runtimes will automatically be cut by about half based on your summer (100%) schedule.