Greenhouse cultivation supports stable crop production but most smart greenhouse systems depend on natural sunlight and are unsuitable for fully indoor environments where all microclimatic variables must be artificially regulated. This study addresses this gap by developing a compact, low-cost indoor smart greenhouse equipped with temperature, humidity, soil moisture, and motion sensors integrated with an ESP32 microcontroller to enable real-time monitoring and automated control of ventilation, irrigation, and ultraviolet (UV)-enabled grow lighting. A wooden-acrylic enclosure was constructed, and a unified control algorithm was implemented to maintain optimal indoor conditions based on sensor feedback. Functional evaluation confirmed reliable sensing performance, stable data synchronisation, and accurate actuation. The system was further assessed using a 10-day cowpea (Vigna unguiculata) growth experiment, during which plants grown inside the greenhouse exhibited healthier early-stage development than those grown outdoors. Quantitative analysis showed a mean absolute percentage error of 37.66% and a root mean square error of 3.27 cm between the greenhouse and natural growth curves, indicating a substantial improvement in growth consistency under controlled indoor conditions. These results demonstrate that it is possible to fully regulate the indoor microclimate to enhance early-stage crop growth, supporting the application of low-cost smart greenhouses in indoor agriculture.