Central Texas landscapes can thrive with much less irrigation. A number of Central Texas’ most popular plants don’t need supplemental irrigation during drought. A 2015-2016 study tested the drought tolerance of 96 ornamental species under four different irrigation regimes: 0% Potential Evapotranspiration (ETo), 20% ETo, 40% ETo and 60% ETo.
Plants were established for four months under irrigation at 100% ETo. Following that, they underwent 12 weeks of drought under one of four ETo irrigation treatments, followed by four months recovery under normal rainfall (December 2015 to March 2016). Growing beds were mulched. A rolling pole barn prevented rainfall from irrigating treatments in the 0% ETo beds.
The work was led by Amy Uyen Truong, Texas A&M AgriLife Extension Service assistant with the Texas A&M Institute of Renewable Natural Resources and the Texas Water Resources Institute in College Station.The four-month establishment period “is key to drought-tolerant landscape success,” Amy said.
The water board estimates outdoor water use accounts for 22 to 50% of total residential use in Texas. Reducing outdoor water use could make a big impact, Amy said. Better understanding which plants need how much water will make a big impact while allowing homeowners to maintain an attractive landscape.
Plants were selected using landscape guides from the cities of Austin and San Antonio as well as top seller lists from Milberger’s Landscaping and Nursery (San Antonio) and Joss Growers (Georgetown). Only plants that were available at the time of the study were planted.
The list included horticultural selections like pink and red Knockout roses as well as colorful Texas natives like Tecoma stans (Esperanza shrub) and the graceful Bouteloua gracilis (blue Grama grass).
Most plants were attractive and healthy using less irrigation water; some looked great with no irrigation.
“The difference between the 0% ETO plot and the 20% ETo plot was striking,” Amy said. “With just a little bit more water, we found that half of the plants were significantly more lush. Some plants don’t need much water to thrive.”
The normal irrigation practice is to irrigate at 70% ETo. But watering at 20 or 40% “resulted in many plants remaining lush and aesthetically pleasing,” she said. “Multiply those potential water savings across the vast amounts of residential and commercial landscapes in Central Texas, and the savings would be significant.” More than half of the plants were stable or “lush” at 20% ETo. About one-fifth (21%) of tested plants “could withstand a period of drought without any supplemental irrigation or rainfall,” she said.
Native plants like Leucophyllum frutescens (cenizo), Symphyotrichum oblongifolium, Nassella tenuissima and introduced species like Guara lindheimeri and Nerium oleander “could work well together in a water-wise landscape” with no additional water after establishment.
As a matter of fact, two plants, the ornamental, Nerium oleander and Texas native Bauhinia lunarioides (Anacacho orchid tree) performed best in all four of the watering scenarios.
The study was supported by AgriLife Research, San Antonio Water System, the cities of Austin and Georgetown and the San Antonio River Authority.–Texas A&M press release.
NewTerrain January 16, 2017.