Growth and water use of garden roses in two climates in the Southwestern United States

Roses are considered high water use plants although little is known about their quantitative water use in different climates. The objective of this study was to determine growth and water use of two cultivars of landscape roses in two locations in the Southwestern United States. Rosa L. WEKbepmey [Strike It Rich™ (SIR)] and RADtko [Double Knock Out® (DK)] were grown in 15.5 L containers in a substrate consisting of 60% compost and 40% soil to simulate a well amended garden soil. From July to November 2008 plants were grown in Tucson, Arizona (32°1649 N 110°5645 W) in a retractable roof greenhouse and in Overton, Texas (32°1739 N 945831 W) outdoors. DK was the larger of the two cultivars and produced 132 g shoot dry weight averaged over the two locations versus 92 g shoot dry weight for SIR after 16 weeks. Average shoot dry weight of roses in Arizona was 130 g and in Texas 92 g. The greater growth rate of plants in Tucson, Arizona, a semi-arid subtropical climate, is likely due to warmer temperatures in fall which supported continuous shoot mass increase until mid November, while the growth rate in Overton, Texas, a humid subtropical climate, was slower throughout the study. Reference evapotranspiration (ETo) was 30 to 120% greater at most sampling dates at the Arizona compared to the Texas location. Water use per plant was approximately two to three times greater in Arizona than in Texas and water use per leaf area followed this pattern. Water use of plants was significantly affected by climate, specifically temperature, but was not a direct function of local reference evapotranspiration.