Abstract: Different concentrations of ferrous sulfate (0.2, 1.0, and 2.0 g/L) were applied through foliar spraying to systematically analyze their effects on the growth and leaf physiological indices of Rhododendron ‘Red Tiara’. The results showed a concentration-dependent effect of iron fertilizer; the 1.0 g/L ferrous sulfate treatment significantly promoted biomass accumulation, plant height growth, and root development in Rhododendron ‘Red Tiara’, with total plant biomass increasing by 21.6% compared to the control. In contrast, the 2.0 g/L ferrous sulfate treatment inhibited growth, significantly reducing total root length, root surface area, and soluble sugar content. The SPAD value was highest under the 0.2 g/L ferrous sulfate treatment, while no significant differences were observed in soluble protein content among treatments. In conclusion, 1.0 g/L was the suitable concentration for foliar iron fertilizer(ferrous sulfate) in Rhododendron ‘Red Tiara’, while excessive application might induce iron stress.

Key words: Rhododendron ‘Red Tiara’, iron fertilizer, growth indices, physiological indices