A commodity RFID system is used for automatically measuring levels of soil moisture in planting containers. A large number of planting containers are used to grow pots in soil in a greenhouse. An RFID reader interrogates passive RFID tags affixed to the planting containers. The RFID reader can be attached to a robotic arm configured to move above multiple rows and columns of containers. Signal features (e.g., MRT, RSS, DMRT) of specific passive RFID tags affixed to specific ones of the containers are automatically monitored, based on the wireless interrogation of the specific tags by the reader. Soil moisture levels of specific containers are then automatically determined based on the signal features of the attached RFID tags, and effects of soilure moisture on electromagnetic fields of antennas of passive RFID tags.