Response of Selected Greenhouse Ornamental Plants to Alkalinity in Irrigation Water

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.

Keywords:

• Sodium bicarbonate
• water quality
• vinca
• chrysanthemum
• hibiscus
• rose
• ivy geranium
• floriculture

ACKNOWLEDGMENTS

The authors express their sincere gratitude to Yoder Brothers Inc. and Colorspot for providing plant material, grant support from the Texas Ornamental Enhancement Program and The Fred C. Gloeckner Foundation, Inc.