Understanding crop root growth and distribution and soil water depletion under water deficit conditions is critical for developing sustainable production practices for cucumber (Cucumis sativus L.) in semi-arid regions like West Texas. Therefore, this study's main objective was to investigate the effect of deficit irrigation (DI) and biochar application on soil water depletion, root growth and distribution, and water productivity (WP) of cucumber. A two-year field study was conducted at Quaker Research Farm, Texas Tech University, Lubbock, TX. A split-plot design was used to randomize four irrigation levels I1 [100% crop evapotranspiration (ETc) throughout the growing season], I2 [80% ETc during early growth (crop establishment to mid-season), 60% ETc during late growth (mid-season to maturity)], I3 (60% ETc during early growth, 80% ETc during late growth), I4 (40% ETc throughout the growing season) and three biochar rates (0, 15, and 20 t/ha) in main-plots and sub-plots, respectively. Results showed a decrease in root length density (RLD) and root surface area density (RSAD) under DI treatments compared to control (I1). RLD was reduced by 24, 4, and 29%, whereas RSAD decreased by 24, 31, and 44% in I2, I3, and I4, respectively, compared to I1. There was greater soil water depletion under the severe DI treatment (I4) without enhanced root plasticity, with some occasional water storage in mild-DI treatments (I2 and I3). The crop water use decreased significantly by 17% in I2, with the least yield penalty of 14% compared to I1. The I2 was the most water productive treatment compared to other DI treatments. Although biochar showed some positive effects on RSAD, it had marginal effects on soil water depletion and water productivity. This study suggests DI strategy optimized soil water depletion by regulating root adaptations or compensatory responses to DI-induced mild to moderate water stress during the growing season, while improving WP for successful cucumber production. It is recommended to test biochar over a longer period (> 2 years) or at higher application rates to better understand its influence on cucumber production and WP in West Texas region.