by Leslie Lyles, MS and Holly Bromley, BS |
The blazing hot days of summer are upon us. While daily temperatures soar and the humidity drops into the 20’s we suffer with dry skin and seek ways to stay well hydrated. We know that drinking plenty of water is essential to good health. Certainly Nevada can be a harsh climate to live in; and not just for us, but for the vegetation that graces our yards. If you look around at the native landscape, it is quite obvious that not many of the plants that grow in our yards are indigenous to our environment. Our landscape plants, like us, depend on plenty of water for good health and in our desert environment that water comes from an irrigation system.
Plants that suffer from persistent drought stress are far more likely to suffer from sunburn, insect infestation or disease and will ultimately not live as many years as they should. But how can you know if your plants are getting enough water?
When new trees, shrubs and perennials are planted, the drip irrigation system is set up so that each plant has one or more emitters running from a half-inch water line. These emitters are calibrated to provide one or two gallons of water each per hour. Therefore, if a new tree has three 2-gallon emitters, then the tree is getting three gallons of water in a thirty minute irrigation cycle. If the irrigation clock is scheduled to come on twice a week, then the new tree is getting 6 gallons of water every week. For a newly planted tree, this is probably sufficient.
After several years the landscape is maturing and everything has grown. Trees that once had small root systems located close to the trunk now have expanding root systems that are radiating many feet from the trunk. The fine hair-like roots that are active in water and nutrient absorption are now out near or beyond the canopy of the tree (very few water absorbing roots are near the trunk.) Thus, the emitters should not be clustered around the trunk, if they are the amount of water the tree receives is woefully inadequate.
It is essential that irrigation systems are updated periodically to keep up with the water needs of the growing landscape. Small perennials usually need little or no adjustment, but larger shrubs and trees are different. They need to have more emitters placed out farther from the trunks so that they are watered on all sides near the drip line where the absorbing roots are. The trick is to adjust the number of emitters so that when the system runs for a set time, each plant gets what it needs.
Another factor to consider is how long to run the watering cycle for the drip system. Lawns need short repeated cycles to prevent run off. Drip systems, however, need to run for long periods to allow a large wetting zone around each emitter. It is far better to run drip irrigation once a week for three hours than three times a week for an hour. Also, the system should be adjusted throughout the growing season so that plants receive more water when it is hot and less during cool weather.
The fact is, plants outgrow irrigation systems and your landscape may be struggling through the heat of summer. Unfortunately, trees and shrubs are very good at hiding the signs of stress until they are weakened enough to succumb to infection or infestation, and by then it is often difficult to return them to health. Applying enough water at the right place for the right amount of time can help ensure a beautiful, healthy landscape for years to come.
References:
- Costello, Lawrence R. et al., 2003. Abiotic Disorders of Landscape Plants; a Diagnostic Guide. University of California Agriculture and Natural Resources.
- Harris, Richard W. 1983. Arboriculture: Care of Trees, Shrubs, and Vines in the Landscape. Prentice Hall.
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