Poor irrigation scheduling is one of the problems regularly seen in commercial and residential landscapes. Plants that get watered for short periods of time every other day or more frequently often develop very shallow root systems. As the weather warms up, soils dry out quicker, requiring more frequent applications of water to keep the plant alive. A better strategy is to apply more water but wait longer in between irrigations. This encourages the roots of plants to grow deeper into the soil where evaporation is less.
Practicing deep-irrigation scheduling may require running your irrigation system for several hours to ensure that water is penetrating the soil to the proper root depth. Irrigation run times of 4-6 hours are not uncommon. Allow the soil around the plant to dry out some before more water is applied. Using this method to irrigate results in healthier plants, with deeper root zones that will better withstand the hot dry summer months of the Sonoran Desert.
Plants that are accustomed to shallow, frequent watering must be changed to less frequent, deep waterings slowly to allow for better root growth so as not to shock or kill the plant. A soil probe can be used to measure how deep the irrigation water has penetrated the soil. The irrigation system itself may need to be modified to ensure an even distribution of water. For example, dry spots appearing between sprinklers on grass may be indicative of poor spacing between heads, sunken heads, or low pressure. The solution is to improve the irrigation system by adding or moving sprinkler heads, or adjusting pressure.
Water Smart Irrigation Tips
Reach Your Roots
Plants have different rooting depths and watering requirements. In general, annuals and grasses have roots extending down up to 12 inches, shrubs 24 inches, and trees 36 inches. Any water applied beyond the root zones is water the plant can’t use. Most desert-adapted plants require less frequent watering than non-desert species.
A soil probe is a metal rod, such as a piece of rebar or a long handled screwdriver, used to measure how deep water has penetrated the soil after an irrigation. Push the probe into the ground after irrigation. It will easily push through wet soil and stop as dry soil is encountered. This provides a simple method to determine if the length of irrigation is sufficient. Periodically check the soil with the probe to determine when it is time to irrigate again. Once the soil is dried out, the probe will become more difficult to push into the ground.
Wake Up and Water
Cooler temperatures in the earliest part of the morning help to reduce evaporation losses from various irrigation systems. This is also usually the least windy time of day, so sprinkler systems will spray water more efficiently.
Watch Your Watering
Leaks, missing drip emitters, or broken sprinkler heads can seriously affect the performance of an irrigation system. Besides allowing water to be wasted, these problems can result in plants not receiving sufficient moisture deeper in the root zone. Since most systems run early in the morning, or at other times when no one is around to look for leaks or other problems, it is a good idea to periodically turn the irrigation system on and observe for problems.
Reuse the Rain
One can take advantage of rainfall to supplement landscape irrigation. Build berms around plants, divert runoff from rooftops and walkways to plants, and use containers to store rainwater.
Make a Cool, Cool Change
Summer heat can make it tough on new plants. New landscape plantings require more frequent waterings to establish strong root systems. If planning to change landscaping, do the work in the cooler months of the year. New plants will do better and need less water to get them established.
Turn On to a Timer
An irrigation timer can help save water in a landscape. Establish an appropriate irrigation schedule for the site conditions and learn how to set the schedule with the timer. Remember to make periodic adjustments to account for changing water requirements as seasons change.
For more information, call Tucson Water's Public Information and Conservation Office at 520-791-4331 .
Visit the website for the Irrigation Association which promotes efficient irrigation technologies, products and services.