In this paper, sliding mode control (SMC) is developed to regulate the water content in the soil. The movement of water in the soil is modeled by the Richards equation, which is a parabolic partial differential equation (PDE). The non-collocated SMC of PDEs is considered, that is, where the sensor and the actuator are at different positions. Two control objectives are considered: the mean water content control, and the water content control at a specified depth. For these purposes, non-standard sliding manifolds are proposed. The existence of the sliding mode in this control system is proved using a Lyapunov function, and the stability properties are analyzed using a frequency stability criterion. Simulation results indicate the excellent transient performance and the complete rejection of external disturbances caused by water evaporation, outperforming on-off and PI controllers. (C) 2018 Elsevier Ltd. All rights reserved.