ABSTRACT Tolerance to alkalinity was evaluated in rose ‘Pink Cupido,’ ivy geranium ‘Peppermint Candy,’ vinca ‘Apricot Delight,’ chrysanthemum ‘Miramar,’ hibiscus ‘Bimini Breeze’ and ‘Mango Breeze’ plants irrigated with solutions containing 0 to 10 mM sodium bicarbonate (NaHCO3). The minimum toxic threshold of NaHCO3 was established as a 10% decrease from the control in chlorophyll concentration (as determined by the SPAD index) and shoot dry mass, which were estimated by using regression models. The ranking for susceptibility to NaHCO3-induced chlorosis was: rose > hibiscus ‘Mango Breeze’ > ivy geranium > chrysanthemum > hibiscus ‘Bimini Breeze” > vinca, with toxic thresholds of 0.8, 2.1, 2.4, 3.2, 4.2, and 6.8 mM NaHCO3, respectively. The ranking for susceptibility to NaHCO3-induced shoot dry mass reduction was: rose > hibiscus ‘Mango Breeze’ ≈ ivy geranium ≈ chrysanthemum ≈ hibiscus ‘Bimini Breeze” > vinca, with toxic thresholds of 2.0, 7.3, > 10, > 10, > 10, > 10 mM NaHCO3, respectively.