Most modern sprinkler timers have a feature that lets you use a Watering Index – it is often called a "Seasonal Adjust" or "Water Budget" feature. The Watering Index (%) modifies your sprinkler controller's watering runtimes. It does this by controlling the watering runtimes for all electric valves managed by your sprinkler controller. By adjusting the Watering Index on your sprinkler controller, all your watering runtimes are either increased or decreased. The adjustment is effectively a percentage (%) of the maximum watering runtime allowed by the sprinkler controller for each valve. As an example, if you water for 6 minutes in summer (at a 100% Watering Index), a 50% Watering Index setting would reduce sprinkler runtimes to 3 minutes.
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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.
Use the chart below, along with site conditions, to find the right watering index value for your yard! Maximize water savings by using the Green Drought Value as a starting point and go up from there.
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.
Summer runtimes are defined as having a 100% Watering Index value. You can use your existing summer schedule that you may have already set up. View the Set Up a Base Watering Schedule page for specific information on how to do this.
The Watering Index (%) is a tool to help you adjust watering times for the current weather. The Watering Index (%) suggests when adjustments should be made, but you have to be proactive by paying attention to the health of your landscape. If your plants look stressed after setting your Watering Index (%) on your sprinkler controller (i.e. “Seasonal Adjust” or “Water Budget” feature), then make practical adjustments from there based on what your landscape is telling you. You may increase the Watering Index (%) slightly, or if the issue is specific to a certain sprinkler valve, go back to the sprinkler controller and adjust the runtime for that zone.
For help on how to program your sprinkler controller, consult your controller's instructions, view videos on how to adjust your specific type of sprinkler controller, or also view the Set Up a Base Watering Schedule page.