Response of two coast redwood (Sequoia sempervirens Endl.) varieties to moderate levels of salt and boron spray measured by stress symptoms: Implications for landscape irrigation using recycled water

Coast redwood (Sequoia sempervirens Endl.) is a popular evergreen tree in landscapes of California and the Pacific Coast States of the United States and Western Canada. Two varieties, Aptos Blue and Los Altos, were tested firstly for tolerance to sodium chloride (NaCl) and boron (B) spray and then in landscape setting when irrigated with recycled water. The NaCl and B concentrations used in the irrigation water were moderate, 500 mg NaCl L−1and 2 mg B L−1. Sodium chloride and B stress symptoms were recorded using image analysis. Aptos Blue was found to be more sensitive to NaCl and B than Los Altos. Sodium (Na) and chloride (Cl) accumulations were not affected by the addition of B in the irrigation water and vice versa, but stress symptoms were additive. The information generated by this study revealed several useful management guidelines. (1) There are salt and boron sensitivity differences between the two coast redwood varieties. Therefore, it is possible to select coast redwood varieties with increased salt tolerance for recycled water irrigation. (2) Coast redwood should not be planted in landscapes where in close proximity to the seacoast. Salt concentrations in the undiluted seawater are much higher than those used in this study. (3) For existing coast redwood plantings, irrigation with recycled water should be restricted to under the canopy of the plants or at the ground level and should be closely monitored to ensure that soil salinity does not exceed 2 dS m−1.