Spring frost injury to blossoms has been a severe problem in pistachio-harvesting lands of Iran. Use of mineral nutrients has been offered as a measure to alleviate or prevent frost harm. The objective of the present study was to investigate the effects of potassium and zinc application on the spring frost damage of pistachio flowers. Treatments included applica-tion of three levels of K2SO4 (0, 1, and 2%) combined with three levels of ZnSO4 (0, 0.5, and 1%). The mineral solutions were sprayed on trees two times (bud swell stage and green tip stage) in 2017–2018. Excised 1-year-old twigs were collected during full blooming. The twigs were exposed to three different low-temperature tests (0, − 2, and − 4 °C), and physiologi-cal and biochemical changes were evaluated. The most concentrated mineral solutions, especially, 1% K2SO4 + 1% ZnSO4, increased significantly freezing tolerance, the content of soluble proteins, soluble carbohydrates, total phenolic compounds, proline, guaiacol peroxidase, and catalase enzyme activity of flowers. Compared with control, the application of K2SO4 in combination with ZnSO4 decreased hydrogen peroxide (H2O2) and malondialdehyde (MDA) concentrations of flowers after freezing tests. The results of the present study could have implications for improving the freezing tolerance of temperate fruit trees cultivated in cold regions by the use of potassium and zinc.
