Relative salt tolerance of selected herbaceous perennials and groundcovers

In order to use reclaimed water to irrigate landscape plants and minimize damage and loss, salinity tolerance of commonly used landscape plants needs to be determined and characterized. Eight herbaceous perennials and groundcovers were obtained from a local nursery, transplanted to 2.6-L plastic containers and grown in the greenhouse for 2 weeks before saline irrigation at electrical conductivity (EC) of 0.8 (tap water), 3.2, 6.4, or 12 dS m−1 were initiated. Plants were irrigated with measured amount of saline solutions to obtain 30% leaching when approximately 50% water had been depleted. After 12 weeks, four plants in each treatment were destructively harvested and dry weights of shoots and roots were determined. Three Penstemon species (P. eatonii A. Gray, P. pseudospectabilis M.E. Jones, and P. strictus Benth.) and Lavandula angustifolia Mill. at 6.4 and 12 dS m−1 and most at 3.2 dS m−1 did not survive. Shoot dry weight of Delosperma cooperi (Hook.f.) L. Bolus decreased by 25% at 12 dS m−1, but there were no significant differences among the rest of the treatments. All plants of Teucrium chamaedrys L. survived but growth was reduced significantly with lower visual scores as salinity of irrigation water increased. Although growth was reduced in Gazania rigens (L.) Gaertn. as salinity increased, no other signs of stress or injury were observed. Ceratostigma plumbaginoides Bunge had reduced growth at 3.2 dS m−1 and higher EC levels compared to the control, older leaves showed reddish pigmentation at 6.4 dS m−1, whereas those at 12 dS m−1 did not survive. Ion concentrations of shoot and root tissue at the end of the experiment on surviving plants were also affected by salinity levels and varied among species. Among the tested species, D. cooperi and G. rigen indicated a relatively high tolerance to salinity, T. chamaedrys and C. plumbaginoides were moderately tolerant, and the rest were less tolerant.