This study evaluated the effectiveness of black plastic mulch in mitigating water stress and its economic benefits in lemon balm (Melissa officinalis L.) cultivation. The experiment was conducted using a split-plot design based on a randomized complete block design with three replications. The main factor was plastic mulch at two levels [No mulch (NM) and black mulch (BM)], and the sub-factor was water stress at four levels (FC100, FC80, FC60, and FC40). The results indicated that water stress significantly reduced leaf area index, biomass, dry matter, water use efficiency, and photosynthetic pigments (chlorophyll a, b, total chlorophyll, and carotenoid content). Application of black plastic mulch mitigated the negative effects of water stress, enhancing plant growth and physiological traits. Economic analysis revealed that the highest net NBPD (Net profit per drop) and B/C (benefit/cost) ratio were obtained under mild water stress (FC80) combined with black mulch. In addition to improving yield, the use of mulch enhanced the economic feasibility of lemon balm cultivation. Therefore, integrating optimal irrigation management with black plastic mulch application can be recommended as an effective strategy to improve yield, water productivity, and economic profitability in lemon balm cultivation, even under humid climatic conditions.