In the experiments reported here, six-month-old seedlings of 12 different ornamental shrubs were planted in a peat and perlite mixture in 1.2-litre plastic pots.
Each of the shrubs were then watered daily with a dilute salt solution, the strength of which was increased each day until it reached one of three concentrations - 10, 40 or 70 millimolar NaCl. At least 50 per cent excess solution was applied at each watering so as to avoid any accumulation of salt in the substrate.
After four months of treatment, all species had accumulated some salt in their leaves and all had lower relative growth rates than the controls with no added salt. Ceanothus thyrsiflorus, Eugenia myrtifolia, and Leptospermum scoparium appeared to be tolerant of salt as their leaves were not badly damaged and plant growth was not greatly reduced by it.
However, the leaves of Cotoneaster lacteus, Pyracantha 'Harlequin', and Escallonia rubra showed considerably more damage and plant growth rates were significantly reduced. In some species, but not all, the growth reduction could be correlated with the accumulation of either chloride or sodium ions.
The Effects of Sodium Chloride on Ornamental Shrubs by Cassaniti, Leonardi and Flowers (2009). Scientia Horticulturae 122 (4): 586-593. The contents of issues of Scientia Horticulturae and abstracts of papers are provided at www.elsevier.com/locate/scihorti
Dr Ken Cockshull is emeritus fellow at Warwick HRI