<p><i>Populus deltoides</i> is highly sensitive to various abiotic stresses, with drought stress significantly impeding its growth and development. Although exogenous application of silicon (Si) and salicylic acid (SA) has been reported to mitigate drought-induced damage, the effects of individual and combined treatments remain underexplored in Poplar species. This study investigated the impact of foliar application of Si and SA, individually and in combination on morpho-physiological and biochemical traits of <i>P. deltoides</i> under three water regimes: 100%, 50%, and 25% field capacity (FC). The results revealed that plant height, stem diameter, and leaf area were improved under both 50% and 25% FC conditions, following individual and combined treatments when compared to untreated controls. Photosynthetic parameters and total biomass were significantly reduced under water stress, with biomass declining by 20.45% and 37.78% at 50% and 25% FC respectively. However, combined foliar application was found to be more effective than individual treatments in sustaining total biomass, redistributing biomass among plant organs, and enhancing photosynthetic efficiency. Furthermore, treatments demonstrated reduced membrane damage by decreasing relative electrolyte leakage (REL), malondialdehyde (MDA) levels, and oxidative stress, thereby maintaining membrane stability index (MSI). The accumulation of osmolytes in the foliage was also enhanced with the combined treatment. Correlation analysis indicated strong associations between growth parameters, including stem girth and height (<i>r</i> = 0.92), leaf area and girth (<i>r</i> = 0.84), and leaf area and height (<i>r</i> = 0.79), highlighting their interdependence under drought stress. These findings demonstrated the synergistic effect of Si and SA in improving drought resilience in Poplar, and thus offer a promising strategy for sustainable agroforestry management in water-limited environments.</p>