By Kelly Feehan, UNL Extension Educator
It is not unusual during summer to see yellow lawns or perennials, and other plants dying back for no obvious reason. Yellowing turfgrass and plant decline is often the result of, or exaggerated by, too frequent or too heavy irrigation.
Overwatering is a Common Homeowner Mistake
When it comes to landscape irrigation, much water is wasted. Some estimates are that lawns and landscapes are overwatered by 30 to 300 percent. Based on my experience over the last 30 years of visiting with homeowners and looking at lawn issues and dead or dying trees, this is a fairly accurate estimate.
Overwatering not only wastes water, a valuable but limited natural resource; it is also unhealthy for landscape plants. While lawns that turn yellow tend to recover, valuable trees, shrubs and perennials are often killed by overwatering.
In an article in the July-August, 2011 issue of Water Efficiency, the Journal of Water Resource Management, author Dan Hull shared this comment made by his neighbor: "We keep looking at the wrong end of the problem. We look at the amount of water available for use, instead of checking how much water we actually use and how much of it we waste."
Avoid wasting water by not overwatering lawns and landscape plants. Water will be conserved and plants will perform better and live longer.
Irrigation Amounts and Frequency- Soil Type
Know if your soil is sandy, loamy or clayey. If too much water is applied to a sandy soil, the water readily drains below plant roots. This is wasteful. Incorporate organic matter into sandy soils to increase the soils water holding capacity. Also develop a sense of how much water needs to be applied to moisten the soil just to the bottom of the roots.
Overwatering clay soils can result in saturated soils. Plants roots require oxygen and will not grow or function well in saturated soils, hence plants decline. Plants grown under these conditions can even wilt. This condition is known as wet wilt. The soil is wet, but unhealthy roots are unable to take up enough moisture.
Overwatering clay soils can result in water running off. Water does not readily soak into clay soils that are low in organic matter and are compacted. If water is applied too rapidly, runoff occurs. This is wasteful and can lead to water pollution.
Irrigation Amounts and Frequency- Plant Needs
Know your plants and their water needs. It is helpful to know the typical depth of plant root systems. An efficient watering will not wet the soil below this depth or water will be wasted. As a general rule, moisten the soil of lawns about 6 inches deep; perennials 6 to 10 inches deep, and trees and shrubs 8 to 12 inches deep.
It is also important to avoid too shallow irrigation. Shallow irrigation does not encourage plant roots to grow as deep and the roots become less efficient at using deeper soil moisture; hence may require more frequent irrigation.
Keep in mind that most plants do better when grown in soil that is a little on the dry side. Many native and well-adapted plants will do fine on average rainfall once they are established. Watering any plants, especially low water use plants, too often will cause them to decline and is a water waste.
Monitor Your Irrigation System
Know your irrigation system. Understand how much water is applied during one setting and the rate at which it is applied. Monitor the system while it is running to be sure it is watering uniformly. Too often the entire irrigation system is run for one or two dry spots and the rest of the area becomes overwatered.
Lawns and landscapes are also overwatered when automatic irrigation systems are not turned off during rainfall. This can be avoided by using an inexpensive rain sensor. Rain sensors are irrigation shut-off devices that keep automatic sprinkler systems from running during and after a certain amount of rainfall.
Research has shown rain sensors can save 17 to 24 percent of irrigation water. By shutting off irrigation systems during a storm, lawns are watered by rain instead of with treated drinking water. Rain sensors conserve water and help avoid overwatering that leads to unhealthy plants.