In Thailand, “Tabtim Siam” pomelo production is essential for domestic consumption and export. Among several environmental factors, soil moisture is the most important factor for citrus plants’ growth and their fruit quality. During the main developmental stages of these plants, the required soil moisture should be above 70% (no water deficit). Therefore, keeping soil moisture at ≥70% in pomelo orchards is crucial. This study developed an IoT-based smart watering system that efficiently monitors soil moisture and assists in maintaining soil moisture at the required level even at a high temperature inside a pomelo orchard in Pak Phanang District, Nakhon Si Thammarat Province, Southern Thailand.