Innovations in Agronomy and Their Impact on Greenhouse Vegetable Yields: Species-Specific Perspectives

Tomato, cucumber, and sweet pepper represent the backbone of greenhouse vegetable cultivation. Over recent decades, developments in agronomic practices have been central to improving yield, resource-use efficiency, resilience to abiotic stresses, and product quality. This review synthesizes dispersed evidence on water and nutrient management, cultivar improvement, grafting, canopy management, biological inputs, and postharvest-oriented agronomy, while highlighting that the three crops exhibit markedly different responses to these practices. These responses are primarily driven by crop-specific differences in source–sink balance, root-zone regulation, canopy architecture, reproductive stability, and postharvest metabolic regulation. Tomato typically demonstrates substantial improvements in yield and water use efficiency under optimized fertigation strategies, with canopy management additionally promoting source–sink balance and stress resilience. Cucumber, by contrast, is particularly sensitive to water deficits, salinity, and nutrient imbalances, necessitating stricter control of irrigation and fertilization to maintain stable root-zone water flux and transpiration dynamics. Sweet pepper often exhibits greater physiological complexity, as yield stability is strongly influenced by microclimate-sensitive metabolic and ionic balance, frequently associated with trade-offs in quality, including firmness, color development, and nutritional composition. The success of grafting, microbial inoculants, and biostimulants further varies considerably among crops, reinforcing the need for crop-specific strategies rather than generalized approaches. Postharvest-oriented agronomy, involving the regulation of nutrient supply, harvest timing, and canopy structure, is becoming increasingly important for prolonging shelf life and improving quality in line with market demands. Sustainability-oriented practices, including nutrient recycling and water-saving strategies, additionally contribute to reducing environmental burdens while maintaining profitability. By identifying species-specific physiological constraints and agronomic priorities, this review highlights that crop-customized and physiologically integrated management strategies are essential for improving productivity, resilience, and quality in protected cultivation.