Response of selected greenhouse ornamental plants to alkalinity in irrigation water

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' approximate to ivy geranium approximate to chrysanthemum approximate to hibiscus 'Bimini Breeze" > vinca, with toxic thresholds of 2.0, 7.3, > 10, > 10, > 10, > 10 mM NaHCO3, respectively.