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All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Permission for printing and for reprinting the material contained herein has been obtained by the publisher. S oil acidity infl uences many chemical and biological reactions that control plant nutrient availability and element toxicity (Sumner et al., 1991; Lavelle et al., 1995). Worldwide, soil acidifi cation affects an estimated 30% of the total topsoil (Sumner and Noble, 2003). Furthermore, 75% of acid topsoils are also affected by subsoil acidity, and failure to address topsoil acidity may result in subsoil acidifi cation of even neutral to alkaline soils (Sumner and Noble, 2003).

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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.

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