No quantitative data exist for greenhouse and nursery cultivation of Crataegus opaca Hook. and Arn., a potentially new fruiting and ornamental Rosaceae species in the USA. In view of increasing reliance on low quality irrigation water for the production and use of woody ornamental crops, we studied the influences of supplemental Ca 2+ on containerized seedling growth and the net uptake and root-to-shoot transport of Na + and Cl − of C. opaca exposed to high-Na + irrigation waters in a greenhouse. After 9 weeks, irrigation solution salinity up to 2 dS m −1 with moderately high NaCl salinity (10 meq l −1 added to the solution) did not lower the total seedling relative growth rate (RGR), nor did a highly sodic solution (sodium adsorption ratio, SAR, of about 50) at 1.5 dS m −1. However, increasing the solution salinity above 3 dS m −1 without supplemental Ca 2+ (SAR of about 100) markedly affected root function. This irrigation treatment increased root Na + concentration and the net uptake of Na + per unit of root dry weight by 3–4 times above the control solution, induced a net loss of K + from roots, reduced the root RGR by over 50 times below the controls, and reduced average evapotranspiration by nearly twice below the control. With this solution, leaf Cl − concentration approached 12 mg g −1 dry weight and marginal and apical leaf necrosis was observed, consistent with earlier reports involving a diversity of Rosaceae members. At an equivalent concentration of applied NaCl to the culture solution (25 meq l −1), absence of supplemental Ca 2+ was more inhibitory to growth, water use, and ion uptake selectivity as compared to inclusion of Ca 2+, despite which, through CaCl 2 supplementation, increased the total solution salinity and Cl − concentration by over 30%. Results suggest that both Cl − and Na + contributed to growth reduction, but provide evidence that Na +-induced root impairment had a primary role in bringing about the growth reduction and high leaf Cl − accumulation.