Bedding Plants Responded Differently to Salinity Stress

Bedding plants are extensively used in landscapes in the United States. As high quality water supply becomes limited in many parts of the world, recycled water is being encouraged to irrigate landscapes. Therefore, information on salt tolerance of bedding plants is of increasing importance. Seedlings of ten species were transplanted to 2.6 L or 10 L pots containing potting mix according to their mature sizes. Plants were grown in a shadehouse with a shade cloth of 25% light exclusion and irrigated with solution at 1.5, 2.5, 3.5, 5.0, or 7.0 dS/m created by adding salts to tap water to simulate the composition of local reclaimed water. After three months of treatments, shoot dry weight and growth index were reduced by elevated salinity. The magnitude of reduction varied with species.  The salinity thresholds in which growth reduction occurred were 3.5 dS/m for angelonia cultivars and ornamental pepper ‘Calico’, 3.5 to 5.0 dS/m for helenium, helichrysum and plumbago. Shoot dry weight and growth index of ornamental pepper ‘Black Pearl’ and vinca ‘Titan’ decreased linearly as salinity level increased. All plants survived, regardless of treatment, except for ornamental pepper ‘Purple Flash’. The mortality rate of ‘Purple Flash’ was 17%, 17%, 33%, 50% and 100%, respectively, when plants were irrigated with solutions of 1.5, 2.5, 3.5, 5.0, and 7.0 dS/m. Since mortality occurred at the beginning of the study, elevated salinity may not be the sole cause.  Physiological responses such as ion uptake, osmotic potential, and cell membrane stability to salinity treatment varied with species. Further studies are needed to confirm the relative salinity tolerance of these species obtained from this experiment.