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The authors investigated salinity tolerance of four intermountain western United States native (Penstemon palmeri, Mirabilis multiflora, Geranium viscosissimum, and Eriogonum jamesii) and four common (Echinacea purpurea, Lavandula angustifolia, Leucanthemum ×superbum ‘Alaska’, and ×Penstemon mexicali ‘Red Rocks’) ornamental herbaceous perennials. Each was irrigated with a solution containing 2 CaCl₂ : 1 NaCl (m ratio) at salinity levels of 0 (control), 1000, 3000, and 5000 mg·L⁻¹ during two 8-week experiments. They measured weekly visual quality and gas exchange and final shoot and root dry weights. Mirabilis multiflora, L. ×superbum, and L. angustifolia maintained high visual quality and 100% survival across salinity levels. However, dry weights for L. ×superbum decreased at salt levels ≥ 3000 mg·L⁻¹ in both experiments and for L. angustifolia in one experiment. Mortality rates of 12% to 100% were observed for the remaining five species irrigated with 3000 and 5000-mg·L⁻¹ solutions. Visual quality of P. palmeri, G. viscosissimum, and E. purpurea varied with time of year the experiment was conducted, with low visual quality associated with high temperatures and light intensities, whereas dry matter and gas exchange responses to salinity were similar between the two experiments. Penstemon ×mexicali and E. jamesii exhibited high mortality, low visual quality, and low gas exchange in the case of E. jamesii at high salinity treatments regardless of when experiments were conducted. Based on visual quality responses, M. multiflora, L. ×superbum, and L. angustifolia are relatively more salt tolerant, and P. ×mexicali and E. jamesii are relatively more intolerant, than the three other species. Penstemon palmeri, G. viscosissimum, and E. purpurea exhibited intermediate tolerance to salinity with acceptable quality during periods of cool temperatures and lower light intensities.

Although salinity is becoming an increasing concern for landscape plants in many areas of the West, few studies have been carried out to evaluate salinity responses of ornamental plants, especially herbaceous perennials. We investigated salinity tolerance of four traditionally grown and four Intermountain West native ornamental herbaceous perennials. Penstemo×mexicali `Red Rocks', Leucanthemum×uperbum `Alaska', Echinacea purpurea, Lavandula angustifolia, Geranium viscosissimum, Eriogonum jamesii, Penstemon palmeri, and Mirabilismultiflora were irrigated with water containing a mixture of 2 CaCl₂: 1 NaCl at salinity levels of 0.33 (tap water control), 2.2, 5.4, and 8.3 dS·m^-1 for 8 weeks. Growth, visual quality, and gas exchange were assessed. Mirabilis multiflora and L.×uperbum `Alaska' showed high salt tolerance based on visual quality. No noticeable leaf necrosis was observed for either species at any salinity level. However, over the 8-week period, growth rates for L. superbumwere reduced by 35%, 58%, and 72% compared to the control for the 2.2, 5.4, and 8.3 dS·m^-1 salinity levels, respectively. The decrease in growth did not reduce visual quality. Growth rates for M. multiflora were slightly higher than the control for the 2.2 and 5.4 dS·m^-1 salinity levels and dropped about 20% at the highest salinity level. Echinaceapurpureashowed the lowest tolerance to salinity, as evidenced by substantial margin burn at all salinity levels as well as high mortality; all plants in the highest salinity treatment died.