• A simple and scalable fabricated hydrogel with multiple functionalities to realize self-sustainable outdoor monitoring solely by it for large-scale applications in precision agriculture.
• Stable direct-current output without requirement on stochastic or temporal environmental energies, achieving an energy density of 1.36 × 10^7 J m−3 with continuous operation of 56.25 days in normal outdoor environment.
• Self-powered noninvasive leaf relative water content monitoring and environmental sensing to evaluate plant health status with high durability and self-recoverability in severe environments.
• The multifunctional hydrogel enables self-sustainable outdoor systems with scalable and low-cost production, paving the way for future agriculture.